The first which is the obvious is let us block while dual wielding, now I understand blocking while dual wielding is not an entirely effective way to block but its better then blocking with your arms while a pack of wolves bite your flesh. So yeah blocking needs to be in, WITH a chance to be disarmed and get your weapon knocked out of your hands depending on the force.
Another option is bringing back everyone's "favorite" skill which is acrobatics. The ability to roll or backflip in oblivion was the difference between life and death, and its absence in skyrim doesn't change that fact. Apart from obviously looking cool, it is very fundamental for certain types of characters like the rouge or assassin. So I think this should seriously be looked at for the next TES games. And will make dual wielding weapons very solid.
Another thing that needs work is the kill moves. Their is a very small amount of actual killmoves for dual wielding weapons. Forget the different weapon types, just dual wielding kill moves are lacking. It looks very awkward to see a killmove designed for a one handed weapon used for someone who is dual wielding weapons.
The combined attacks when using both weapons simultaneously is very few for animations. Seeing the same animations get old really quick, it would be nice if bethesda had a pool of attack animations and the game randomly picks any of those attacks to keep in fresh.
In the end the dual wielding weapons mechanic is one of the weakest combat aspects of the entire game. And I hope someone from bethesda reads this to take this into consideration when doing the next TEs.