Just because you can only have 2 things equipped at once out of spells, shields, and weapons doesn't necessarily mean that any particular style of play will suffer. The loadout feature will make it easy to swap between spells still, but with the addition of being able to swap weapons and shields as well. So if you're a 2-handed fighter, you can still switch from that to healing spells, you'll just have to swap your loadout to do so real quickly. Or better yet, if you face an opponent you could better take on by using one-handed weapons and a shield, you can use a loadout switch to swap to that.
This could very easily increase the difficulty of the game, but I think the Elder Scrolls desperately needs a real difficult bump. Oblivion's difficulty was largely manufactured and tedious, not strategic and tactical.
I thought combat was especially crappy in Oblvion. It felt like everything had way too much HP, magicka costs didn't scale properly for the strength of spells, and enemies basically took cheap tactics to whittle down their massive stockpiles of health.
I'm very excited for dual wielding, I always thought it was a fairly neat style of combat, even if it isn't particularly realistic, but I'm not worried about realism in a game that lets you slow down time by shouting phrases in old dragon speak.