... I think it would be extremely cool to transfer the money you found in World of Warcraft to some other Online-Role-Game - also the providers could earn via provision - so: why is this not?
You can do it since 2002 with d2jsp.org
I used to exchange my money between many mmorpg and make profit.
Maybe I was not clear enough with d2jsp.org :
1 - You sell your virtual money or any service from the game (ex: WoW) for forum gold (FG)
2 - You exchange your FG for an other virtual money in a different game (ex: diablo III)
You just transferred money from WoW to Diablo III.
The most traded games are : diablo 2-3, runescape, WoW, path of exile, guild wars 1-2, LoL, realm of the mad god, ...