As far as restrictions go, we already know there will be restrictions based on what the job in question can already equip (ie. can't transmog mage armor onto tank armor, etc) and that seasonal gear will be restricted in some manner. Other than that, who knows?

As for the Odin armor though, I imagine they can simply make it so you transmog it to a chest piece and when said piece is equipped, it visually covers all other slots.