Really want a magic tank

[Malkria]

I don't think a ranged tank would work at all. But it could be close range spell caster, I think a lot of blue magic spells would lend themselves to that quite well.
Blaster could be a close range spell, 1000 needles, bad breath and aqualung are all suitable for radial or cone AoE attacks.

It would have to have some melee attacks, like Red mage, blue mage has never been a pure caster, so it could be amalgamated with spellblade attacks, which I think would work well in the context of a magitek knight.

Again, not necessarily. There are plenty of ideas across the mmo genre that could allow for a variety of tanking. For example using a gun and shield ala Guild Wars 2 or the mesmer from the same game. To does require some outside of the box thinking which may be hampered by how much the devs are trying to keep all the jobs functioning about the same in the 1-30 range. But not impossible.

I mean simply try it in some dungeons. It isn't the best tank, but you CAN see it working if given a more dedicated job and/or abilities. Just depends on if the devs want to try it, but you can see the potential if you try it yourself.