Edit: The more I think about this, the more I like it, actually. As a PC gamer, I was afraid that, if I wanted to play a right handed sword-and-shield character, I'd have to attack with the right mouse button and block with the left. Hopefully now that it's only right handed, it'll be opposite hands/mouse buttons, like Oblivion.
I think these are all the possibilities...
Nothing || Shield/Torch
The tweet just confirmed this isn't possible. Left hand only.