Alright so we have 8 chapters left for FEHs, since the standard number of Chapters in a Book is 13. So heres the theory part:
Now we're getting Three Houses Later this year, and since 3 houses has 3 lords, it's easy to assume that we'll get 3 banners for this game easily, 1 for each of the Lords, and the Avatar will accompany the Lords on the banner, they'll milk as much content out of them, likely us getting about 18 or such units from it
So 3 banners seems easy for them, these banners going to be for Chapter 10, 11 and 13
I'll get to Chapter 12 later
Now for the next few chapters
Chapter 6-9 will all be different games. One will belong to Mystery of the Emblem, since we had that Gharnef GHB back in Nov 2018, it's like a reverse for Lloyd when he joined Heroes, as he joined in May 2017, 2 months after the FE7 Banner. I believe this banner will be either Chapter 6 or 7.
Now that leaves 4 more banners
1 Banner is gonna be another Laguz banner, likely introducing the Cats and such
We have like 1 Wolf Laguz, good amount of Birds, but no Cats, Lions or Tigers, so this is a chance to bring them in
I see this in May, so likely Chapter 8, give us a little break from Laguz content, so we don't get more right away
That leaves 3 more chapters. Now the last 2 are gonna be hard. 1 will belong likely to FE 4 or 7 as both are really popular, whilst the other one will likely belong to Awakening, these banners will more so be filler.
Now for the VERY last one Chapter 12, this banner being in early September, I believe this banner, will be a Thracia banner. On September 1st, Thracia will be celebrating it's 20th Anniversary, Heroes does give something small for Game anniversary's, and since it's a big one for a game, we'll likely get a banner for Thracia during this time
And thats my Theory, I believe these will be the banners for this year