As you know, many BIS items on many classes are a diferent type of armor as your class would normally use so tmogs looks horrible, specially if youre full tier tmogs.

Examples are:
Leather hands/belt on fury warriors
Cloth legs used by boomies/hpalas
Leather hands on frost DKs
New meta adriana's on rets
Leather rs10hc hands on rshamans and so on.

Im asking for only upgrades like leather into plate but not the other way arround.
Ofc keep it so you can only tmog equipable items so we don't get priest looking like DKs