I like to make my character look a certain way because I like that appearance. Not for anyone elses gaze. Compliments are nice of course but they're the last thing I'm going for when I sit there and piece together a new look.
Resources are arguable. This would be settled by the actual demand for the feature. If this is something next to nobody wants then fine, don't waste the precious SQUEENIX DEV HOURS™.
Self Expression. This removes no self expression other than needing to know that absolutely everyone has to "experience" your particular expression if you're in their party or on their screen.
Immersion breaking mismatched gear would be solved with normalized job AF or generic placeholder glamours. This also solves people directly wearing unglamoured pieces. You could also drop entire placeholder character models if people cannot stand the idea of "their" character in clothes they didn't pick.
Lore excuses are lame, I agree.
People who like glamour or enjoy not looking default don't have to use it. Glamour would still be a thing for a lot of the playerbase and new designs would be used. I don't understand why this isn't obvious. It's a proposed option, not a new gamewide enforced thing.