I mean, you'll still be able to tank various 4man dungeons/content just fine, even as a DRK/WAR/GNB, right?. So, it shouldn't matter if you're MT or OT.

It's safe to assume that their own job gimmicks dictates how they'll be played in the future? If a Paladin has to take damage to counter or perfect-counter, than it makes sense that he gets the MT role.
A Paladins whole identity is about keeping your party safe with defensive abilities and white magicks etc.

Im going to reserve an opinion about the other 4 tanks.