I thought of three things:
A) WebKit: Burn it to the ground and remake it. We need fewer specific WebKit tags and more sticking to the standards. With any luck, it could even make it leaner and faster if they trim the code enough.
B) Change the iPad Safari UI. It's not unfriendly, but could be less of an obvious desktop metaphor and more touch friendly. Metro I.E. was pretty good at that.
C) Metal 2.0: It needs to work better than what we have now and maybe even better than OpenGL.
Those are just some things that came to mind.
Shouldn't screen size be a factor with multitasking?
General a new Safari Ui would be awesome for ipad/iphone