While I don't like the look of them myself, capes do have a certain FF pedigree. <3 those 8-bit caped crusaders.

Other than the aforementioned physics problems, there could be conflicts with existing gear, a lot of gear is spiky with large pauldrons (especially Darklight Tank gear and heavy darksteel) which would clip horribly and a lot of gear already has hoods (cowls) that would make hooded capes look silly.

I think capes would have needed to be in from the beginning, I think it may be too late to implement them now.