The issue with the economy and those 1% (Haha political jokes aside) that have gold cap, is that eventually, anyone is capable of reaching gold cap, for the simple fact that you run out of shit to spend your money on.
Example: I Pvp exclusively, so my repairs are minimal/non-existent. I cap out weekly in arenas, then run all the raids from Cataclysm->WoTLK, Occasionally I'll do some BC runs but that's more for mogs/pets since the wardrobe is going to be a thing and my completion-ism is starting to tug at me for it. Add in the daily grind of the Garrison, and the flipping of garrison resources to gold, and on top of all that, I cap my honor as often as possible, and dump it into those daggers. All of this makes a recipe for slowly pooling a large quantity of gold.
What do I have to spend all this gold on? Pets? Mounts? Gear? Play time? Eventually there's a cap to all of that (Except play time, and even that has a arguable cap based on availability) but you see the issue, eventually, people will stop having things to spend money on, and we will all reach the cap, and when everyone is gold capped, no one is, and this is just using myself as an example, let alone the auction house baron's with multiple gold capped toons all with guild banks just so they have a PLACE to store all that gold.
There needs to be a mechanic introduced that allows players to spend their gold, yet it must also not give a stat bonus so that it doesn't equate to gold/money=Skill.
I've recommended they introduce player housing. It's something that seems easy to me. They could even make it similar to the garrison.
You buy a small, medium, or large plot which varies in price by gold, and the larger plots, give you the choice of more furniture/features.
Each plot can be purchased in each major race area but you can only have one plot at a time (Exodar, stormwind, orgrimmar, etc.) If time saving is a thing, make it so the architecture is set dependent on the races zone (That way a night elf house isn't placed within say the undercity)
Each home can have "Plots" but instead of small, medium, and large buildings, you free form it. Allow someone to build a bed, a dresser and a night stand for one small home, mean while, a large home, can have a library room, a bed, etc.
Cut the player home off from trade, but place it in the major cities. This will draw players to the racial cities, permanently, while also not allowing them to accomplish everything from that one hub. Close enough to the major city that you can handle your business, but secluded enough to make it your own.
Make them visible for a flyby, but phased on the inside, so that when a player flies over the city they get that joy of "This is my home" and when they come to that home, it is uniquely theirs. This also eliminates the issue of having to expand the cities for the sake of multiple player spots.
For further gold sinking, allow the purchase of specific arbitrary NPC's. Examples being a barber, a shirt vendor, a common goods salesman, maybe a repairman. No auctioneers, no bankers, nothing that can pull someone from the main city.
This solution would allow someone with tons of gold, to sink it into making an amazing home, while also not creating something that causes the every man to hate the folks who are wealthier.
This solution is also easily sustainable as you can make new items I'd imagine simply, given a starting template, and then improve on it. Perhaps by making specific furniture be rewards for achievements and such (Nothing to the extreme like, getting a sock drawer for downing a mythic boss, but say "Made it to level 10, here's a sock drawer")