What I want is for the game to stop dropping the good ideas they had for less amazing new ones.
Most importantly, BRING BACK GYM LEADER REMATCHES. They were the best part. I still play emerald and the best part is when you have a gym leader with a solid balance of pokemon from each gen, and they 7th and eighth gym leaders are stronger than the champion, so you can train your higher level pokemon.
Also the battle frontier in emerald is well done. It works because it doesn't really have to add any plot, but it gives you actually CHALLENGING battles. You need good movesets and EV's. I honestly don't give a crap about how my character looks, if I wanted to play dress up, I would just buy SIMS...
And I like the idea of a legendary thats not some dragon dual-type... Cause they are running out of options with that.
A visit to another region, preferably a previous one would be cool. But I am just reiterating that.