Add me to the choir but the creative potential for a class being able to transmogrify their gear to any armor type would be profound. Since we have the warband unlocks now for unlocking gear, how difficult and plausible do you think it would be to implement, or rather, remove gear type restrictions for classes?
Also have you ever created something with the Wowhead wardrobe that was cross gear? What was it?
They’ll never remove xmog restrictions and rightfully so.
People cry about lack of class identity now, but this would just completely kill what little remains
So being able to mix and match gear with an ice/cold theme from mail and plate to add onto a frost mage would ruin what it means to be a frost mage?
I think this would be good for RP sets for visual purposes. For those saying RP sets aren’t that necessary, well neither is RP player housing 
right? 
Code the “grey” items to be able the do this (give the grey items purpose to collect). It would be of course purely cosmetic and drive up replayability immensely and make total use of your Tmog collection, especially for those with alts of other classes. To be fair and not create drama with collectors and higher level players only make cross mogging possible with old expansions not gear in the most current one. Just suggesting a possible solution, not the end all or laying down the law or road map by any means. 