I've made over 100k profit just npcing my allagan pieces from level 1 to 40 and I only started taking them after level 20 and I had good dungeon gear. Secondly, why people are removing farming from a way to make money is beyond me. I sold random junk from a night of fate runs that dropped of mobs for over 10k gil. Even if the ah took 5% I still made 10k gil and way more than if I had vendored them.
Farther more the end game content isn't out yet. And if it's anything remarkably close to FFXI there will be ways of generating large quantities of gil from unique/rare items in the various dungeon modes and hard modes. And theres likely to be some sort of crafted item needed to do a certain part of the end game content at some point, which will sell for a lot.
But imo, the economy will go up rapidly as a character is capable of generating over 200,000 gil in allagan pieces from quests. So if 7000 people on a server do that, that's 1,400,000,000 gil....