I don't understand why they're so reserved with what they include from other canons when the "game canon" is an extremely inconsistent mess, especially when going from the Classic Era to Adventure Era, or Adventure Era to Sonic '06 onward (and even '06 to the Meta Era / Children's Dreamworks Comedy Era). There has very obviously been no sense of quality control when it comes to the storytelling or characterizations in the games for over a decade. The storytelling and characters haven't exactly been what I'd consider quality since starting to get fleshed-out more from Adventure and onward, but since the Meta Era it's only somehow gotten worse. The Adventure titles, Heroes, and the Sonic X canon were at least something I can accept and kind of get interested in, even if they're not my ideal vision. The writing / art direction became so uninspired and bland from Unleashed and so-forth that you'd think these writers don't even care about Sonic, which puts them on par with the situation Ken Penders was in. Even Penders managed to be more interesting though, which is sad.
It seems like each mainline installment is beginning to come jam-packed with a new retcon or inconsistency, further confusing the fanbase. It's just an absolute mess of shit that most people don't even care about or enjoy. I think the best course of action would be to just retcon pretty much the entirety of 'Modern Sonic' and drag it back to where Adventure 2 or Heroes left off, since that's the variant of post-retro Sonic that people actually care about and have been begging for. How many people actually really want elements of Shadow TH, '06, Story Book Series, Unleashed, Colors, Generations, Lost World, or Forces to remain canon and referenced? (I'm aware some of those are said to be "retconed", but still)
Elements of Sonic X could also be included in this hypothetical 'Adventure' continuation, as I believe enough people actually appreciate the original version of that show. In this situation, Retro Sonic should just remain its own universe and not crossover with Adventure Sonic whatsoever as that creates divide in the fanbase, and it's generally just a lazy Sonic Team tactic of trying to please everyone in singular low-effort games. Both Sonics can have their own storylines, supporting characters, 2D titles, 3D titles, spin-off titles, comics, shows, merch, and whatever else. Boom Sonic can just die off because it's basically Meta Era Sonic in Ratchet & Clank land with an over-detailed unnecessary design change and a Back At The Barnyard CGI comedy show. There should also be better titles to distinguish the series' / universes of Retro and Modern since it's pretty odd to give them age-related labels.