This discussion topic comes up every now and again whenever new class sets are revealed.
It has been made abundantly clear over the last 20 years of this game that what we wear on our characters is the paramount of player agency and expression. Not too far off of real life, really. More than mounts, more than pets, a lot more than titles. Transmog is the gateway between you, behind your keyboard, truly being immersed with the little character sitting in the middle of the screen… BUT,
Legion also showed us how effective and important classes are as part of that expression. When you pick a class, you’re not just picking a gameplay style (professional players somewhat exempt)- you’re picking a whole wardrobe. An entire aesthetic. The visuals, the gameplay, the associated NPCs, the identity- it’s no secret why Blizzard kept pushing the phrase “class fantasy” heavily during the build up towards Legion’s order halls. It’s also why class tier sets eventually found their way back into the game. It really does matter to people.
There is an agency to having exclusive access to certain armour per class. Yes, you can transmog armour of the same proficiency, which means being able to sometimes make look-alike mogs; like a Warrior decked out as a paladin or DK- but it’s never a guarantee you’ll get access to the full set in the same way the actual class does. And taking that exclusivity away does many things to make a player’s commitment to a single character feel less valuable. And that’s important in a game where you want to keep players around and emotionally connected to their characters. A very real consequence of completely removing the transmog limitations would actually be a fading/absent loyalty to a certain class longterm, for example.
Why bother playing anything else if I can just make my Warrior look like a Monk? or a Rogue? It also kills the at-a-glance recognition that other games like League of Legends or HotS heavily depended on. Without seeing a tooltip, without seeing a class colour, if you’re seeing something wearing leather w/ 1 handed weapons, you already can access the microsecond neural link to potential classes, abilities, and strategy that are associated with it. Seeing a character fully decked out in the Fire-Charm vestments set (Monk Tier 15), with a 2h staff suddenly charge at you and beat you down with death magic and 0 use of martial arts isn’t too far from the same feeling of shock one gets from being given a coffee cup filled with orange juice. Your brain expects one thing, but upon having that anticipation betrayed, you fumble for a second.
Wild comparison, I know. But when you combine that lost feeling of exclusivity of access to what your class can wear, combined with the greater gameplay ramifications, it just creates more bad than good. There’s so little to gain here vs so much to lose, because at the end of the day, there are cosmetic sets for everybody- and then there are class sets. We differentiate them because the former are not aesthetically hinged to a single class (mostly).
All of that in mind? Personally, I’m of the opinion that certain sets should be allowed across the board on a case-by-case basis. Old sets? Sets that aren’t class locked? Or maybe limiting another class from wearing more than a set number of transmog pieces that belong to another class? There can always be a middle ground, but I do think in the long term it would open the flood gates and make any new sets lose some appeal.