I'm hoping for this layout, since I play on the 360:
RT: Attack with right hand
RB: Block with right hand
LT: Attack with left hand
LB: Block with left hand
Of course I have no clue what blocking with a spell would be like... perhaps a utility spell can be set there, while a combat spell would be set to the trigger? (a destruction/restoration spell would be combat, unlock/feather would be utility for example)
Okay there are some flaws with this, and I'm not sure how that would work on PC, but I think this could possible work with some tweaking.
I think this would be better.
RT: Attack with right hand
LT: Attack with left hand / block(If using a shield)
RB: Block(Dual Wield) / parry / shield bash(If using a shield)
LB: Move objects around like in Oblivion.
Edit: Or LT could be shield bash and keep RB as block to avoid confusion...