Dual threat has a flat proc rate, so dual wield does work better with it. It’s likely that we’ll use dualwield in the first season partly for that reason, but eventually the better scaling on 2h will probably overtake it again.
You should be able to mog the artifact weapon on two one-handers.
I was using the WW artifact weapon (fist weapons) appearance on my polearm as WW in season 3, so I am certain you can do the same on Brew regardless of your weapon type.