Depends on the goals here. Power level your professions for 1, 2, or 3 characters? Drop a ton of coin on BOEs? Tons of raid consumes for week one of raid launch?
Professions probably won’t be so bad unless you REALLY want them maxed out right when you hit 90.
Gear? A lot of pre-bis really comes from dailies and heroics. Some from professions here and there. Its a little less sinky here than Cata imo but close enough. I would expect to take a hit here.
Special mounts? Yeah you are going to want a good chunk of change for these if you “gotta have them all” and even more if you “gotta have them all, now”. No other way around here.
BMAH… its going to be a knife fight on this. You are going to have people that no life GDKP slaved for expansions worth of gold with several gold caps going for things on there. I think even being rich af is going to be less a factor than just having the will to drop the bag on single items for a lot of things on the BMAH.