That's less likely to be a code limitation and more a "the weapon design/modeling team is working on other content right now, and we consider that higher priority." (I would bet, for instance, that right now the weapon design/modeling team is working on hashing out the general aesthetic of this expansion's relic weapons.)
Things like "the server coughs up a hairball and then falls over dead if multiple people open a glamour dresser in the same spot" or "the glamour system breaks entirely if you move a glamour dresser while you're using it"? Those could easily be due to spaghetti code.
Say, for instance, that the cache of glamour items is tied to the record of the in-world object being used, versus the character. There are many reasons this could be the case!
But then if you move the in-world object (i.e., removing it and recreating it elsewhere), the glamour record goes "poof" while being used. That would be Bad. Or you have four people using the same glamour dresser, and as a result of it having 1600 glamour items loaded into the in-memory record of a single object, it exceeds what was ever supposed to be the maximum object record size in memory, and Bad Things Happen.
And "there's no feasible way to change this without cutting out a giant chunk of the zone instance servers to rewrite it" could 1. absolutely be a real problem in trying to implement glamour dressers in the world in general, and 2. could absolutely be the fault of the aforementioned development issues. Be it spaghetti code ("some of this is built on code where no one really knows how it works anymore"), or legacy code that you just can't change because 47 different things depend on it doing things one way, so even if you cut the legacy code out and rewrote it, you'd then have to rewrite the other 46 things as well. Stuff like that.
(The latter isn't technically spaghetti code in the traditional sense, but there's still a fairly large overlap; sometimes the reason you can't cut the thing out and replace it is that because the thing in question is spaghetti code, no one is 100% certain how it works. Thus no one is certain that replacing it with a newer function won't break the other 46 things.)