Cross server auction houses might be cool. Even a united economy might be alright... One of the main reasons I don't play horde on my server is because their economy is ruined. Low pop on horde side so wool is 40g a stack, hardly any selection in the first place. Go on Alliance side get whatever you want no problem.

I think it would lead to more balance. It might be World of WARcraft but even the USA trades with hostile nations daily. Anything to balance the horde/alliance sides would be great- not saying this would but it could not hurt.