What they SHOULD do (as an economist) is give people the option to put their own gil (OT TOMES!!!) in as a reward to the in-demand class. You are a BLM, you need Praetorium, you put up 40k of gil, the tank sees in dungeon roulette there is a potential reward of 100k for doing a dungeon (your 40k plus 60k more from the other 5-6 people willing to pay for the run), and the tank goes, "Oh nice, let's rock this!". That would provide incentive for the tank to queue, for the tank to do well to finish the dungeon (he only gets a % based on how far the group gets), and it would avoid inflation because gil wouldn't be being pumped in, just exchanged.

Of course there would be the issue of cross-server gil exchanges and legacy players willing to spend 600k on something a normal player would only want to spend 10k on, but randomization and supply/demand equalizing should eventually smooth out.