Until literally no group takes you because that combo is a fraction of the DPS of warlock/mage or priest/mage, and none of your paladin abilities are worth hitting because the GCD would be better spent on a mage ability, and your standard rotation involves completely ignoring one of your classes because it just isn't worth the GCD to disrupt the mechanics of the higher dps one for anything other than a major CD.
This palyerbase couldn't even handle being asked to pick two abilities and some passives, and you dorks think adding an entire second class toolkit wouldn't just be an absolute shitshow?