I have no idea how long it would take, I have only programmed little things, I can't even imagine lol. But I'm betting it would be a looong process and they would never give up on ORAS to make that a thing for S&M unfortunately
Though I think it would be reasonable for them to make it a bit more difficult by giving gym-leaders teams with better stats and moves... You know, just make it a little bit more challenging without having to go all out.