Well you need some stamina & regen to block ofc but magicka tanks are indeed viable for templars. Imo, it's the best way to go for a templar tank.
Just don't get aggro on everything, otherwise your stamina bar will be struggle. Thanks to the repentance, you can replenish your stamina bar when things die. But that requires having good dps in your group.
So it's kinda group effort to make this build workBut it's totally viable.
I think there may be couple builds in tamrielfoundry.com. Check it out.
NO! it worked wonderfully before this update. But zos is now officially destroying this playstyle by nerfing stamina regen while blocking. They are doing this because of pvp playing getting pissy because they CANT KILL A TANK SOLO. Hint hint....they should not be able to kill a tank solo. You sacrifice so much damage by being a tank, now that you can't block and regen tanks will be just as squish as any other dos glass cannon class, even still without the damage needed...this change has infuriated me so much, that has been my play style for the past year, now nerfed because nighblades are ***