Since SL is giving a much needed facelift to character creation and the motif of SL seems to be choose your own adventure style with covenants; it got me thinking, this is like the perfect expansion to go all the way and remove an archaic barrier.
The biggest hurdle obviously being druids, but I think it would be fine for them to retain their exclusivity since they're already supposed to be the 'special class.'
We've seem numerous times that races can deviate from their racial class group, I think its time for players to be able to do so as well. As I see it the concern is over classes losing their identity but in current WoW, Trolls can be Paladins and Humans can be Shamans so I feel that ship has already sailed.