I had a enhancement shaman be my tank up through level 63. I think I did a full clear of BF and Ramparts at level 62. It definitely isn't easy, but if you like the challenge I say go for it. I loved pvping w/ the 1enhance 4 ele combo outdoors, but inside a battleground that enhancement shaman is doing more harm than good. I dropped my fifth and now just roll 4 *elementals in the bgs.

*typo