So a question: Most tanks have two forms of active mitigation: Physical and proactive (shield of the righteous, shield block, blood shield, etc.) and magical and reactive (word of glory, shield barrier, death strike), etc. My question, could you think of a proactive AM ability that would be unique? (Fury Ward by the way, is not very unique on its own right now).
SP/AP has been done (paladins), obviously extra health armor and crit immunity are (relatively) easy to tune and add, glyph needs to be gone. So my opinion: the actual demon model (not the crappy wings one) should be used for a tank form and possible a non-tank (maybe only some dps spec) form. Personally I still think that the wings model should be a glyph (and just the model!) for all specs sort of like Treant Form.
Having not really touched DA itself with a 10 foot pole, what would be unique about this compared to other tanks? Not in terms of look but playstyle?