It's improbable, but I'd like to see a more strategic use of weather, in terms of field alteration, or even just aesthetics. Say, using Rain Dance immediately after Sandstorm to turn the field to mud, which would benefit Water and Ground types and slow everything else down. Or using Sunny Day after Rain Dance to create a rainbow. It'd just be nice if there was actually a sign on the battlefield that there had actually BEEN a weather anomaly, rather than just the same standard background for that area.
Taking that one step further in terms of aesthetics, I'd quite like to see some damage done to the surrounding area to reflect attacks, as well. Say something uses Flamethrower and misses...have it blast a nearby tree. Something uses Explosion and leaves a giant hole in the ground. It'd just be entertaining to see, and make battles more involving.