Well there was more (not more, but the fact that it was included and was different enough) than enough in Gen 2 which had even less overall space sooooo...
And it could be just like, a less fleshed out version but if it's set in an alternate universe that could explain why the fighting-type guy is there instead of Surge. The marks on the wall definitely add up with the gym though and unless it's a new feature to battle past gym leaders in their old gyms I'm definitely leaning towards Kanto exploration.
And then with Sinnoh remakes next you'd theoretically be able to explore Johto post-game too, thanks to Sinjoh ruins! It definitely makes sense if these games feature Kanto and next ones Johto. Then ideally Gen 8 and Unova remakes would be on 3DS so every region would get to feature on 3DS...
...hopeful! :)