That might be inconvenient for people who actually do want to share glamours between classes. And TBH 15 plates per class seems like a lot. It would be 420 extra plates per player, which will have nontrivial requirements for server capacity. And I don't think the intent is to allow players to store every gear set ever as glamours either.

I have an alternative proposal: If memory serves, the gear sets already save the glamours used for the set. Make that accessible as a glamour plate instead. There's one set available per class plus a few extra, so that should take care of basic per-class customization. And since it uses data which is already stored, it shouldn't require anything extra from the servers. When you update a gear set, the game would ask if you want to also update the glamour plate for that set, or apply the previously saved glamour plate to the new gear. The current 15 shared glamour plates would be retained of course.

Also, please allow changing glamours outside of cities when a gear set is associated by a glamour plate. It really diminishes the usefulness of the association feature if you can't count on it always working.