Don't forget, the Hoenn map also has a bunch of unused/inaccessible islands! Not that it really means too much right now but it's definitely possible to expand to them if it means the mainland not getting too cluttered.
Are you talking about an introduction to the Frontier? They could just advertise it on TV or something after you arrived back home after the league. I loved watching TV to check to see if friends' achievements, the 'special' promotions, etc. showed up after mixing records and everything.
Having the old contests split up again seems like a much better idea anyways because, like someone mentioned before, the tents lacked purpose really, imo. It was also a nice touch to have to travel to get to each level of contests instead of cramming them together if you ask me.
Speaking of the retro contests, one would hope that they allow online, like has been mentioned before. I preferred the old over Gen IV's.
Why does Pokemon availability have to play an importance there, haha? We also had everything available in Gen III(in some way) before HGSS rolled around but that didn't stop them. There's always been ways to get every Pokemon really.