I'd really like to see some kind of modular system for the sequencing side of things, like AudioUnits but to replace the piano roll, so people could create their own wacky sequencers. Like a tracker style interface or whatever.
I know you could sort of do that already by routing midi from one program to another but thats not ideal.
Even better would be modular EVERYTHING, like buzz but with plugins for the sequencing as well so you can choose piano roll/drums/tracker or whatever you want.
At the very least it would be nice to see proper support for developers to extend live by officially opening up the python stuff underneath (on OS X as well as windows!) and letting people make their own live plugins.