Well, the question pretty much speaks for itself.
As a long time fantasy lover, I've always loved the Arcane Warrior/Mageknight Archetype. I personally would love to see a class like this in WoW, and to me, it seems like the next logical Hero class if they decide to make another one.
First of all, the tools are all there. We have caster plate, which only 1 of 30 specs use at the moment, the only gear variation to have so little use. We have caster 1 Handers, and we have Caster shields. Give the new class the Hybrid talent that converts Spirit to hit, and we're already pretty golden gearwise, and we'll get more use of the Caster plate and shields.
Secondly, I imagine the two other specs as Melee DPS and Tanking. A lot of people seem to think a new tanking class/spec would solve the problem of tank shortage, and while I don't wholeheartedly agree with that point of view, a new tanking spec would at least not hurt the possibility of a rise in Tank numbers. I imagine the Melee spec as somewhat akin to the current implementaion of Enhancement shamans, combining melee and spells.
Thirdly, I think it gives a possibilty for a truly unique class thematic, and a very unique feel.
so, TL;DR: If you ignore the bad taste many still have in the back of their throat after the DK Balancing issues at the start of Wrath, would you like to see a Plated Caster hybrid as the next hero class?