I've got no reason to believe Sonic Team are going to move on from their sloppy engine and worsening takes on the boost gameplay style when Forces sold well enough despite mediocre reception. We'll see the same outdated models, bland art and shallow gameplay that's all spectacle with no substance. Forces did nothing if not prove that SEGA do not have any idea (or that they don't care) what their audience wants. There was no effort put into making it a solid game there; it was a cynical plea to almost every fraction of the split fanbase. Fans who liked the early-mid 2000s games got their "dark" story with lots of characters and edgey new villain, Classic fans got Classic Sonic to play as, modern fans got the boosting and then there was the avatar for the huge subset of fans who make their own characters and just the general popularity of personal expression in games these days (there is of course overlap between these groups). None of these features are close to being fleshed out, and particularly in the case of the boost and Classic gameplay styles, they took the already flawed gameplay of Generations and proceeded to make it worse. I don't believe that these were conscious changes made to improve the games that some people disagree on, but rather were the result of an inexperienced team with poor direction, poor vision and poor understanding of what they even wanted to achieve. The choice was to make a bunch of things that looked like they were what fans wanted, and they didn't go to any lengths to really deliver. The gameplay was phoned in and lazy.
Whatever Sonic Team try next, I don't think they'll be appealing to fans such as myself. They'll continue to go after thd lowest hanging fruit, rather than making a quality product that will appeal to a broad audience because requires more time and money (and the right talent).
I can't comment on the content of the game, like additional characters, story or even gameplay style. They might move on from the boost, I guess? But even if they do, I'm really sure they won't do it right. Lost World was a mess, as were the avatars and Classic Sonic in Forces. It'll be a low quality game.