Wouldn't it be really hard to do a Sinnoh remake at this point in time? ORAS changed RS pretty significantly and people weren't huge fans of that. Now with gen 7, they've got more in-depth story/cutscenes and a completely different gridless overworld style, which means many overworld puzzles (for example sliding ice puzzles and strength puzzles) from older regions are now completely irrelevant. The way Pokemon games are structured now is completely different too, and they've even removed HM's.

Considering how ORAS played out, and how much more changes we've seen in Gen 7, I think it's time to accept that the concept of a "remake" isn't as relevant as it used to be, and any "remakes" coming from GF in the future will be significantly more detached from its source material, just as ORAS was further away from it's source material than HGSS was, and HGSS was likewise with FRLG.