So wait, is this complaining about a lack of armoury chest space, or a lack of space for glams? I can't tell if this is a legitimate concern about not being able to have the space for Reaper gear, or just Yet Another General Complaint About Glam Plates.

I have gear for every job to 80 and I have no issues with armoury chest space. Sucks that you'd sooner deprive yourself of an opportunity to play a new job you're ostensibly interested in rather than actually try to address your inventory/hoarding issue, but SE is not exactly to blame for your choice here. If you cared enough, you could make this work.

There should also be more more outfit spaces beyond the fifteen that we already have, considering that there are a LOT of jobs in the game.
We were clearly never intended to have one individual plate for each class. And if the rollout rate on additional plates is anything to go by, I wouldn't expect to eventually have one for each class, either.

Regardless, this issue can be gotten around by not putting class-specific gear on your plates, but coming up with some more general sets that multiple classes can use.