I hope that duel wielding will consider the wight of the weapons into account. if someone wants to weild two longswords let them (IMO i think it sounds stupid) but they should move slower then someone wielding two daggers. ooh I just had a cool thought what if you had to block in the direction of the attack, so if you had a sword on your right hand and shield on the left and a guy attacked from the right blocking with your left hand wouldnt have an effect, but if you blocked with your right you could counter attack with a shield bash. that would make combat way more fun.
On the topic of longswords vs daggers, there is no reason to penalize longswords. If you have played Oblivion then you will know that daggers do not get any special privileges. They are fast and short. Very lethal with enchantments or poisons. Two just makes them total enchant blasters. Try to imagine some uzi-rings from Morrowind (rapid-fire high damage spells/switch rings after blasting every guard in the world). If you know how to play, those daggers could be much more lethal than those longswords.
As for dual weapon blocking, I'm guessing that you will be blocking with both weapons simultaneously.
Purely speculation on the controls. I just made this up:
Lmb =Left attackRmb =Right attackAlt/Mmb =Block
If you had a shield in your left hand, then blocking would still be done with ALT, and the bashing with Lmb. I'm not sure why people think that you need 4 buttons. Why would you be attacking while blocking? Everyone would just tank behind their shield.