One feature that would be very attractive to the masses, would be to offer a simple interface for changing the entire "skin" of a slider. A drop-down menu, perhaps with a small preview, would allow users to choose between
minimalist etc. Of course, they all suck :) but you can find plenty of other slider elements on the web, some of them quite jaw-dropping. When you start working on this, hit me up and I'll provide some examples.