I have barely any gold myself less than 1k atm, maybe i can farm a few 1000 before tbc releases but i'm sceptical about how much impact it really has, there are ppl who will have enough gold to clean the auction house out of primals and motes, but at some point these ppl are going to be done with the mats they need. to craft whatever it is. you have wayy to many individual ppl farming these different items and either keeping them or selling them on. different classes did need different primals and some classes didn't need other primals so it will move around. the motes and primals I don't need ill sell for the ones I do need etc.
the gold in this game is great for some things but i've never really found it to be the be all end all, you need, 6k for your epic flying skill, a large portion of this can be farmed in BC, you need gold for enchants, and consumables, if you can't just make those yourself. you barely need more than 10k gold in total for gems and enchants on 3 tiers of gear it can't cost more than 3-4k.
if you have a character that can DE, you save money on enchants, if you have an alchemist or a herbalist you can make your own flasks and elixirs, if you do fishing and cooking you have your well fed covered. after this you're spending gold on enchants, and boes for your alts. repairs which can be negligible if you barely wipe. once you've gotten past that 6k epic flying gold sink you're pretty much only going to make gold again because there is no sink after that until wrath.
the classic mats will start to sell again and ppl need stuff to level professions. the first tier of raiding is similar to molten core so, do you need flasks and BiS crafted gear to kill grull/mag and clear karazhan, no you don't. in the same way you didn't need flasks for molten core or BiS crafted gear. if we have t4 for several months then you have ample time to farm stuff assuming you're logging in and playing. most of that first month is going to be, getting to 70, getting your reputations up so you can buy the heroic keys, running heroics. getting attuned to karazhan. this progression doesn't really rely on gold, just you playing the game.