I like the idea of a magitank, as well as some of the ideas in this thread, but you need to come up with ways it'll differ from existing tanks in practice.

Using MP instead of TP, using cloth instead of plate? You're just switching some letters around, maybe just adding a simple mp regen mechanic. In the case of armour, if base def and mdef are the same for all tank classes, whats the point if only for flavour?

What I'm getting at is don't just change the flavour, change how its played. We really don't need another DMG reduction cooldown tank like PLD, alot of people still say WAR is too much like that now.

Now go be creative!

I'm looking forward to see what you can come up with.