I'm not fond of the idea of adding an Akimbo mechanic to the game, it would be a lot of work, but most importantly as a player the balancing issues could be a problem.
If the mechanics not balanced just right everyone will complain Akimbo is broken, if it's too weak they'll say it is crap and pointless.
It will also possibly have a knock-on effect to individual pistols being adjusted around it, making them less viable as secondary weapons.
However, I think having a primary slot with a new "weapon" that was dual pistols could be cool. New pistols that look different to any of the current ones and can be adjusted purely by itself.
Essentially a semi-auto SMG or a carbine, it could then have it's stats adjusted without affecting any other weapon.
This would also allow for a user to equip an RSA or whatever people use as a long range pistol if they wish.