A proper pressure-sensitive stylus from Apple would be nice. Out of the few pressure-sensitive bluetooth styli available from third-parties, only two (Pogo Connect & Jot Touch 4) support palm rejection. Even the prototype pen showed by Adobe during MAX didn't seem to have palm rejection implemented. It just feels really awkward holding a pen without putting the palm on a surface somewhere. The drawings apps on iOS are so good though, and if I have to pick between good hardware/weak software (Android tablets w/ S-pen) and good software/weak hardware (iPads w/ 3rd party pen), I would choose the latter.
Also, the Surface Pro pen apparently had issues supporting Photoshop, and it didn't get fixed until a (beta) driver update released two days ago.