I've suggested Closets on multiple occasions when it comes to additional storage space. Closets are used to store only gear, making them ideal for storing your glamour items that can't go in the armoire. You would also be able to access them at the inn so players who don't have the luxury of housing/apartment/personal quarters available to them can utilize them as well. This would free up a lot of retainer space for just about every player in the game.

As for how much space would they offer? I'm not entirely sure, but I do know that it should increase as more gear is released to the game.