Transmogrification is all the rage on the blue forum trackers (sites that track posts of official blizzard representatives)
I'm a packrat. I like the idea of somewhere to store that armor that I'm likely to never use (eg PVP, DPS).
I won't be changing the look of my gear (maybe with the exception of rediculous plate shoulders), but many others will be.
This means a market for unusual (i.e. old) armour and weapons, as cosmetically oriented players 'gotta catch em all', both in terms of crafted goods as well as paterns. Tailors, Leatherworkers and Blacksmiths with old rare patterns - rejoice. Gather your mats of the AH now while the are cheap. When this goes live, make your goods, and maybe even get your social guildy to dance around in Stormwind/Origmar with the 'retro' look.