Yeah, I agree that I was hugely disappointed that the Battle Frontier and Battle Hill wasn't used (they could have remade the Battle Hill to function like the Battle Chateau, which I've found extremely useful for leveling up Pokemon, not to mention getting rich).
They could've at least used the Battle Tower if they wanted to remain true to the original, but used the Battle Chatelaines to add that flavor. I feel cheated that they teased us with a scale model of the Battle Tower. Arceus only knows how the true Gen III fans must feel. If they add the Battle Frontier (complete with the same Frontier Brains), I'll probably be far more forgiving then the Gen-three-ers. If they don't add that to the Z Version, I wouldn't be surprised if the fans continue demanding for Delta Emerald to happen, until it does. And I couldn't blame them.
And don't even get me started on the lack of those possible double battles, or not being able to re-challenge gym leaders!
/Okay, enough ranting.
I think that there is definitely always demand for this generation, or that, to be remade. After all, by my experience, the generation that you start playing in is the one that you have the strongest feelings for. It all depends on if there is enough demand, to the point that it would be financially feasible on Game Freak's part to even bother.
Anywho, I think that what, if anything, gets remade next (besides the speculative Emerald, which I'd actually be surprised by) will depend on if the next generation used a new game console or not.
If not, expect a Gen I remake. I can see them also making it possible to travel throughout Johto in the post game, so it'll sort of be like G/S/C/HG/SS in reverse (or so I hope. I can't believe that they didn't do that for FR/LG!). That way, Game Freak can also tell the fans "okay, you also got your Gen II remake too, so don't expect to see Johto again any time soon even after we make D/P". If they're going to remake Gen I, they minus well go for broke, and remake both Kanto and Johto. I personally do hope that they do make a game where you set out from somewhere in Kanto, since I never played FR/LG, and the Red version that I got from a friend won't retain it's save file (which I guess must mean that it's internal battery has run dry). That would be for the Generation that is coming up: Gen 7. Either that, or there'll be no remakes for that Generation.
If Gen 7 is using a brand new console, then I expect that Gen 4 will be remade as well, which probably means in 3-4 years from now. If not, then I'd be surprised if we didn't still didn't see them during Gen 8's tenure.