It would be nice to have a bass properly integrated into MIDI - perhaps a long-scale version of the YR1000 is the answer to that, though that then loses the ability to have a native bass sound as well as the MIDI generated notes.
I can't see there being any great change to the basic construction of the bass - the basic concept of a long stick protruding from a wider flat bit is going to stay the same. The two basic methods of combining the stick bit and the other bit, ie. either having the stick bit go all the way along the other bit or have it attached at one end with glue or screws, seems pretty immutable, though there has been the odd instance of a metal frame and suspended fretboard. I can think of three current pickup systems - magnetic, piezo, and Lightwave. I'm not sure that any great advances can be made on those fronts - after all, it's all about sensing how a string is moving.
Seeing as how we all have different ideas about how a bass should look, perhaps the most significant advance that could be made would be to have a flat screen on the front of the body that would show a picture of the bass body that you love most. I suppose I'd better go and patent that then.