In data's to do list he has a checkbox called, Dual Wielding revision, does this mean we can dual wield now?
If so what weapons can?

You've been able to dual wield for a long time, but the issue is that you never really had control of whatever was in your offhand due to clunkiness.

To make something dual wieldable, you just set some variable to 1.

Add the gun to the shields group and buy it from the shields tab in the buy menu.

Needs to be onehanded = 1 as well.

Only problem is that the AI doesn't recognize a "shield" as a weapon.

Works if you have a one-handed weapon + offhand "shield" though.

I don't think that the planned revision is that hard of a job to implement.

This is going to get more into Mod Making than Game Discussion, but I've refined dual wielding a good bit today.
viewtopic.php?p=530673#p530673
Get AZC.rte, then buy a couple Heavy Dualies.

You find or buy two of the same weapon, and convert one to offhand using the pi menu, eliminating the logistics problems with usual dual wielding mechanics.
Once you do this, the script goes to great lengths to make sure that you equip them both at the same time, and reload them both at the same time, eliminating those usual problems for dual wielded weapons. It causes a penalty to accuracy and sight range. You can use the same pi menu slice to stop dual wielding, or dual wielding will stop if either gun is broken or dropped.

I think I've pretty much hammered out the flaws of dual wielding, aside from the following:
--It doesn't have any reloading penalty, because as far as I know, Lua cannot change reloading times. It is possible to deactivate devices for a time after reloading to give the effect of a longer reload, but the AI and UI don't understand that.
--AI also won't start dual wielding, but once you make an actor start dual wielding, it will continue to while under AI control. I know of no easy way to check the quantity of an item in an actor's inventory, so that's why I haven't made initiation automatic.
--When they get converted back and forth from primary and offhand, it repairs any dents. Checking how many wounds there are with Lua would be an unfeasibly convoluted process, so far as I know.
--Alternating between guns instead of firing both at the same time would be cooler.

okay, thank you very much Azukki!