With each new installment of Pokemon, there's always a great deal of emphasis on new features, Pokemon and content. But often to make room for that new content, some aspects of previous generations have to be scaled back or removed entirely.
Simply put, what do you want to see less of in Pokemon X and Y?
First on the list for me is forme changes. I think the developers have taken the idea and run it headfirst into the ground with Gen V, with so many gratuitious and downright unneccesary formes. Drastically reducing the number of Pokemon that can change forme would help make the new forme changers we do get more special.
In a similar vein there needs to be fewer legendaries, especially if we're getting a smaller dex with prevos and evos of older Pokemon. The developers really need to step away from trying to match or top previous generations in terms of numbers. With so many legendaries, they just aren't able to explore them all adequately, and more legendaries steal focus from regular Pokemon in virtually all aspects of the franchise (Games, Anime, marketing/merchandise, the competitive field etc). I'd much rather have another family of regular Pokemon than an extra legendary set.
Lastly, while we know that X&Y will be introducing evolutions of older Pokemon, I'd really like to see fewer than in Gen IV. That leaves much more room for wholly original lines, which I generally find much more interesting.