Oh, okay. Cool. I gotcha. That's why asking for clarity works, folks. ;P
In that case, I'd have to say it's not an impossibility, but the reason they may not opt for it outside of a remake is because an old region has too much baggage or expectation. In a way, Gold/Silver still sorta-kinda did that, as it wasn't a remake, but the adventure didn't start there. I remember people being disappointed with Kanto in Gold/Silver, so if some people were livid back then, I can't imagine how they'd react to a full fledged game of Kanto: The Future. Others, on the other hand, would love it. People being disappointed with change in Pokemon is as old as this franchise.
By starting with a new region, they can write a new story from scratch, and there are no expectations outside of gameplay, and your general subjective aesthetics. They can also introduce a fresh set of new monsters. It's not that they couldn't otherwise, but if most the old ones disappeared to make room, someone's going to complain. A lot of someones. Your best option is to add additionals, and the number is already too high in every region.
If you wanted to approach it as [region]:The Future as a game marketed towards getting older (by when they started and age) fans back into the series, I can't imagine that would work, either, considering they're holding on to the nostalgia of things as they were even tighter. Remakes sort of work better for that.
Maybe it'd make an interesting gaiden game or something, but I can't see it working as part of the series proper. Limitations and risks seem to be what's stopping it from happening.