This isn't really a feature per say...but hear me out. Simply put, a subtle motion blur in camera transitions would make secondlife a much more fluid, and aesthetically pleasing experience. Most high end video games (I'm not saying SL is one, I'm just noting the current trends in this sort of media) have some sort of motion blur, which in my opinion makes a world of difference. Obviously this would be an optional feature, as you would need good specs for this to look nice.
Thanks!
Mizu Frequency