A materia tab would be great as long as they keep materia so it requires inventory slots. I think what a lot of people want is for it to be like how crystals are now but then we'd end up with too much hoarding. Since the server merge, most materia prices have plummeted. There is a large disparity between prices of the higher tier materia and ones with lower quality stats (within the same quality ie. +9 enmity rage IV materia is dirt cheap while +12 are non-existent or absurd prices). This problem would only increase if materia didn't consume inventory slots.

Another way to alleviate inventory space & management issues would be to let us purchase more retainers. I believe the original plan around launch was to allow purchasing of retainers through the subscription service, something like $1 per retainer. In my ~3 years of XI I had at least 2 mules at all times and at one point I was up to 4 (for several months, not just for mog bonanza :P). I hate to jump on the "add this from XI" bandwagon, but I think this would be a reasonable option for FFXIV too.