TLDR - real issue is raid expectations and more specifically expectation to Windfury Totem... for more details, read on -
I've played a shaman tank for a while. I know many shaman tanks and myself have tanked content all the way through Naxx, and have surprised plenty of people with capabilities expanded and adapted for shamen to be able to do that.
While there are plenty of challenges to choosing to tank on a Shaman (lack of cooldowns, complexity of rotation, mana upkeep, ect.), the biggest elephant in the room I wanted to address though is perception and expectation from the shaman. And to be even more specific, the problem with Windfury totem.
Raid expectation from a shaman is to be a raid strength augment, and any shaman that will be permitted to tank will still be expected to drop the most coveted totem of all, you guessed it, the Windfury Totem. This augments the melee DPS of the group by quite a bit.
Here's the problem with this - dropping Windfury provides no benefit to the shaman and in fact robs him 4% crit and dodge provided by the Agi (Grace of Air) totem. This causes a funny conundrum for shaman tank who boosts DPS of his group, which robs him of more mitigation and threat.
Proposal for future enhancement shaman ... enhancements
- let's make a symbiotic relationship that benefits the shaman for dropping Windfury totem - When party members proc Windfury, shaman gains 5% block for 10 secs, stacking 5 times - now there's a good benefit that could be tied to Spirit Armor talent
- let's not forget our Enhancement brothers - When party members proc windfury, shaman gains 50AP, stacking 5 times for 10 secs - this benefit may be tied to Calming Winds talent
- Alternatively both effects can be combined into Enhancing Totems talent and the benefit provided can be tied to wearing a shield or not