I'd definitely love for them to return, as well. Not just that, but to flesh out Pokedex data with new information. Granted there isn't a whole lot to say about some Pokemon, but that's just it; I want to be surprised with something cool or interesting, but a lot of the recent iterations of Pokedex data is just repeating stuff we already know about from previous generations. That's not even counting when they simply reuse older Pokedex data for post-national Dex 'mon (although oddly enough the remakes tend to have new entries for said 'mon, which is a nice touch, let's hope OR/AS does the same!)
That said, OR/AS will likely use their respective entries for the 300+ 'mon that existed in Gen III at the time, at least I assume. I get they were trying to tidy stuff up with some of the Emerald entries, but if you have more space to work with, you might as well use it.