I have exactly zero against players being able to toggle off transmog appearance. That is, unless it would require a lot of work for Blizz. I’m not sure how the programming works, but I’m suspecting it could be possible that that it may require some spaghetti code to solve it. If so I’m against it, but I’m not against the concept, at all, even in the slightest. However…
Wrath was the first expansion where attaining PvP gear became easy. As in, you can expect to gear up fully with honor gear quite qickly. If I remember correctly it was possibly to buy pieces of arena gear every 1-2 weeks or so even at lower rating.
I know that you know this and what I’m going to write here, but I want to lay out the reasoning to make the point salient.
This eliminates essentially all need to benefit from seeing what kind of gear an opponent has in Arena. If you’re higher rating you can assume others have max honor gear and equivalent number of arena gear pieces as you do.
If you’re serious about climbing and need to be evaluating the enemy team’s gear level in arena, then you’d be more interested in being able to see the health and mana pools. Well, the higher you climb the more you’ll assume that whomever it is you are facing they are fully geared.
Looking at the flat number in health or mana means you can estimate what the enemy is wearing in arena. You already do this to see if a paladin is holy or ret, as an example. Say, a hypothetical scenario where you’re 1800 or higher, and a mage has lower hp and more mana than usual, it’s fair to assume that the mage is wearing lots of PvE pieces. Making this assesment by looking at the gear can’t be done even nearly as fast when that mage is on the other side of the arena map behind a pillar.
The only thing I can remember being somewhat important to see is the weapons of a melee. The rest is predictable at higher arena rating, and if someone isn’t doing full PvP gear you’ll see it instantly by looking at the HP bar (as PvP gear has more stamina).
Regarding BGs, I’m struggling to see why it would be of any importance as good players will play according to their gear level. You’ll unconsciously take note if someone is a pro gamer and has the gear to match.
A fragile warrior will be wary to charge in, and a fully geared warrior with lots of confidence in their own ability will be extremely aggressive towards your face. E.g. with abilities introduced in Wrath you’re going to see warriors getting very cocky in PvP due to Bladestorm, charge useable in combat, some self healing, and so on.
If a mage or a hunter is shooting at you from afar you’ll default to assuming they have good gear until proven otherwise. Even a hunter in blues and a few greens taking free shots at you in a BG is dangerous, so you’ll treat them accordingly.
Hot take… I understand the concern, but everyone that opposes transmog in instanced PvP, that doesn’t forget about it, will feel it’s not important enough to make a fuss about on the forum in about a month in or so. People have fairly equivalent gear.
If possible to implement without too much work by Blizz, why not. Win-win.