Sasuke needs to kill Sakura in order to attain the Mangekyou Sharingan.

Sakura's character development is dead, and has been for a very long time. It would make for some VERY nice tensions - it would obviously infuriate Naruto, and send Rock Lee into a murderous rampage. It would show that Sasuke really DID feel something for her and was supressing it the whole time in order to avoid exactly this sort of thing - and she can, tragically, find it out right before he kills her. It would surprise us by downplaying Naruto and Sasuke's "friendship".

And it would shake things up, something that hasn't happened in awhile.