I think materia should be stackable also, but more than this they need to have HQ versions or name them I-XIV of however many different versions there are.

I'm sure we will. It's not coincidence SE increased our inventory during this update or that they told us it was only temporary until they finished the UI overhaul.
This is partly to do with the gear restrictions actually, Yoshida has already said it temporary until they have the mannequin system up and working.