Did you hear? Android P is a thing now. We have no idea what the P will stand for (no, it won't be Peanut Butter and Jelly, unfortunately) and we have very little insight into the changes it will bring because we just got the very first developer pre-beta beta preview. One thing we do know though is that everyone will want it and want it as soon as possible. That's how it works and that's how we are wired. We want updates, we want them to be spectacular and we want them right now.
The reality of the situation is a bit different. Most phones made in the last 18 months will see Android P, but some of them will only get an update to P when we see the first developer preview for Android Q (Quince Jelly or gtfo, Google!) come along. It's a lot easier for manufacturers to update their phones to a newer version, but it's still not any better. That's another article for another time, though. This one is where I guess which phones will get updated sometime in the next 12 months.
Predicting anything Android-related is 10% science and 90% interpretation.
It's not as easy as you think and many sudsy cold beverages worth of thought goes into my guesses each and every year. About one-third of them are no-brainers, but some of the others are basically the same odds as a coin flip. It seems like manufacturers only care about a few models that get a lot of press time. But I do have to toot my own hat (or something) and say I have a pretty good track record. Luck or skill? You decide. (It's totally skill.)
Let's break it down by the major manufacturers of the phones we love and make a few predictions. Remeber, these are just predictions and not any official word on anything from any company. We'll also circle back to once Android P is officially released and see how close I got.

Google

I always start with Google because it's easy and I'll get it right every time. That's what I want at the top of the page. I say it's easy because Google has already told us which phones get updated and which won't.
  • The Pixel 2 and Pixel 2 XL will be updated to Android P.
  • The Pixel and Pixel XL will be updated to Android P.
  • While not actually from Google, any Android One phones manufactured since October 2017 will also be updated.
And that's it. Prior to the Pixel, Google promised two years of full support and three years of security updates for phones they sell under their own brand. Come September or so when we expect to see Android P go gold, the Nexus 6P and Nexus 5X will be just about three years old

Samsung

Samsung makes more models of a single flagship line like the Galaxy S each year than Google has made in total, but it's also pretty easy to know which phones Samsung will update because they're predictable. Samsung offers four "premium" models each year. like 2018's Galaxy S9, Galaxy S9+, the Galaxy S9 Active that we all know is coming, and the Galaxy Note 9. Even when Samsung sold 15 different models of the Galaxy S6, they were all treated the same when it came to expecting an update.
When to expect it is just as predictable, and it will happen about a year from the date this was first published (March 2018). Some models in Europe will see it first, about a month later it will show up somewhere else, and once Samsung is satisfied it's not going to totally wreck about a gazillion phones they will give it the green light. Add in whatever time your carrier needs and the final result is just about a year from its initial release.
  • The Galaxy S9 and S9+ (and any S9 Active that comes in the future) will be updated to Android P.
  • The Galaxy Note 9 will be updated to Android P.
  • The Galaxy S8 and S8+, and the Galaxy S8 Active will be updated to Android P.
  • The Galaxy Note 8 will be updated to Android P.
Here's where it gets interesting. there are a handful of other Galaxy phones that have a huge regional fanbase. In India, for example, the Galaxy J models are huge hits because they offer most of the same experience you find in a Galaxy S at a lower price. Samsung will give them the same treatment the Galaxy S and Note lines receive. That's not the most interesting part, though.
There's a chance Samsung will try to update the Galaxy S7 and S7 edge to Android P. Adding the third year of life to the Galaxy S line would be an important move in a world where only Apple supports more than the last two yearly remakes. And Apple is Samsung's only competition is the mobile space so Samsung would love to erase the stigma of Android phones being disposable. I don't know if Samsung will succeed and get Android P on a Galaxy S7, but I do know they will be trying. They almost have to.

LG

LG has always been a wild card when I write this post every year. Like Samsung, there are a few "important" models that get all the press coverage and plenty of other more inexpensive models that most of us aren't talking about.
LG also mentioned some streamlining in the release cycle, which means the LG G8 won't arrive before most people were able to buy a G6. Hopefully, it also gives the development teams time to get an update out the door and have it be a good update.
  • The LG V30 (including the V30S or whatever models we have seen or will see) will be updated to Android P.
  • The LG V20 will be updated to Android P.
  • The LG G6 will see Android P.
Older models like the G5 and V10 are done seeing any attention and won't see any updates. LG makes a handful of phones that aren't quite flagship material, and we know it is willing to spend the time and money on updating some of them even if your carrier isn't you never see it.
I also think LG consolidating things and releasing phones when they think it's time for a new model rather than by looking at a calendar will make a difference here and lead to longer support.

Huawei

Huawei is tough to read. It hasn't abandoned the Asian way of doing smartphones like LG and Samsung have for their U.S. divisions and sometimes that means the things the company does can be puzzling to those of us used to the Western way of thinking. Just when I think I have figured out exactly which phones are the company's flagship models that will get the lion's share of time and money spent, they change it all up. That's a good thing.
Something made Huawei change the way it redistributes and maintains phones running the EMUI operating system (Huawei's version of Android) in 2017 and I think that's going to be reflected when it comes to Android P updates.
  • The Huawei P10 will be updated to Android P.
  • The Huawei Mate 10 will be updated to Android P.
  • The Honor 9 and Honor View 10 series will be updated to Android P. I'm hoping, but less confident about the Honor 7X.
  • The Huawei Mate 9 will probably be updated to Android P, but we'll see.
This includes the various Plus, Pro, and Porsche models (I want a Porsche phone) as well, and because EMUI is so different than every other smartphone software available users will have no idea which version of Android they are running unless they look.
Besides, if the things a handful of little birds are saying happen to be true, EMUI 9 isn't going to be able to run on any hardware older than what comes in these phones.

Motorola

Motorola had a weird 2017. That's putting it mildly. They released like 100 phones in the Americas and Western Europe (Editor's note: it was actually 9) and they ranged from the surprisingly great $100 Moto E4 to the Moto X4, the first of hopefully many non-Google phones you can use on Project Fi, and all the Z and Force you can handle in between.. And they did it without compromising the G series which has been a company staple for years from the smartphone division.
Moto phones under Lenovo are slowly becoming like the Thinkpad -- quietly chugging along in the background doing their thing. And doing it well.
So far in 2018, we've heard the company is going to release more phones than ever this year and that they were scaling back and had to lay off employees (in the same week, no less) so we're not sure just what to expect. in the coming months. One thing I am pretty sure of is that every one of those 2017 phones, as well as any we see in 2018, will be updated to Android P.
That's right, no bullet point list of the highlight models. Every Moto phone manufactured in 2017 or later will see Android P.
Lenovo has taken a lot of the fanfare surrounding Android version updates away and quietly builds them in the background. Maybe the update horrorshow that happened when the company first absorbed Moto branding made them decide the limelight is a better place to be. Or maybe when you build 100 different models, an update day feels more like a Tuesday than something special.

Must mentions

These may be the companies we're most familiar with in the west that sell Android phones, but they aren't the only companies doing it. Out of the literally hundreds of models available, a few stand out and need mentioning.
  • OnePlus will update the 5 and 5T.
  • Sony's high-end Xperia like the Zs and Xs from 2017 and 2018 will be updated, but other models probably won't be.
  • Essential will have learned from mistakes with Oreo and the EP1 will be fast-tracked for Android P.
  • I'm not sure how changes in the company will affect HTC, but thinking all their phones as far back as the U11 and UBolt will see an update.
  • The BlackBerry KEYone probably won't be upgraded to Android P, but we like surprises!
  • Now that Nokia has committed to Android One across all of its devices, there's a good chance many of the more expensive models, like the Nokia 7 and Nokia 8 Sirocco, will be updated to Android P.
  • Someone at XDA will update their Nexus One to Android P and I am going to do my best to get Google to send that person a brand new Pixel 3 NotchXL.
Like mentioned earlier, these are just educated guesses at this point. but one thing I know for certain is that no matter what the phone, any updates will feel like they took too long to make it into our hands. That's just how we're wired.