I really like the idea of being able to switch between single blade/empty off-hand, double-blade and weapons sheathed to accomodate the situation based on how much i feel I need to rely on magic
. Delicious thought, mmmm... If you're at a distance from a large group of packed enemies, you go for sheathed and the double spell combo. When they're finally close to you, you draw one blade to go "might and magic, baby!". And when you're out of magicka, you draw the second blade to finish the job with brute force.
If they get it right, it will be awesome. I'm really for not letting anyone cast a spell with both hands occupied. Letting a knight with shield and sword in hand cast spells as well as they could do it with both hands free was one of the things that svcked about Oblivion - what was the point of being a mage if you could do magic with a warrior just as well?