Im not sure giving more and more classes ability to 2h is the way to go. I'd rather give them something different. Although it is clear that 2h's are just way stonger than dualweilders, that both give up same defensive stats. (It can be argued that dualweilders have easier time swapping a shield on, but with pwa 2h's can do the same at little cost if they ever feel the need).
Overal dualweilding costs:
40% dmg 1.5*str dmg 2 ab 3 feats (requires twice as many weapon buffs) edit: also smaller dmg brackets vs resistance
gains: 33% more hits (at best, vs harper, cot etc even less) (able to finesse - but who wants those dexters)
So back to my original point, I'd rather like to see something else given to dualweilders, such as dwarven waraxe. Maybe give them some bonuses on umm.. no ideas here.. skill bonuses to parry/disc? bonus dc on kd/disarm?
Anyways, my point being, instead of turning every class into 2h'er, I'd focus on improving the alternatives (also ranged weps!)
edit2: back in the day doubleweps had +2offhand attacks, which made them go to choice, similar to 2h now for those who could handle it. That bonus was deemed too strong vs regular dualweilders, now they suffer similar, but not as massive disadventage vs 2h'ers.