Except that if there
are class restrictions you won't be able to make the WHM look like a warrior because WHM can't equip warrior gear.
We all know someone will complain about restrictions, though this is all dependent on how far SE goes in restricting vanity slots. Blizzard, believe it or not, is REALLY stingy with their restrictions for transmogrification, and has a ton of limitations. Here:
While several don't apply (the "guns to bows" bit, the stuff with void storage, heirlooms and legendaries), the first and the last one would be a very good place for SE to start with. The last one also covers the issue with seasonal gear. Admitedly, I'm iffy on that because on the WoW forums we have some who have been asking for certain gear to be allowed for transmogging (like a certain poster that wants to wear a
Vile Fumigator's Mask full-time but can't because it wasn't flagged for transmog).