One of the biggest gold sinks I've encountered is imbuing. I've got artificers in training on a bunch of shards and even though I try to gather the small gems via mining and hunting, it just doesn't really cut it. So a lot of the gold I do manage to scrape up just gets spent buying up gems and more gems, which are then used up and deleted through the imbuing and unraveling process. As hard as I try, I just cannot manage to get above the 116 to 120 million gold mark across all my characters and across all shards.
If I've finished working on imbuing on some shard, the next thing the gold gets poured into is buying a few galleons with paint and lobster traps. I'd love to see a few more styles of galleons that are a bit more expensive (nothing outrageous) and more vibrant paint colors that cost a bit more than the current ones.
Something else I'd like to see are some enhancements to housing that you would buy for large amounts of gold from an PC and that could be applied to any house, custom or classic, such as some rudimentary type of indoor plumbing (a pump for running water in your kitchen?), other types of fireplaces or heat and light sources, etc.
I'd also go for temporary pet dyes that you could purchase in-game from an NPC, as long as the colors were not too ridiculous.
I'd also be willing to spend massive amounts of gold at an NPC garden center/nursery on various kinds of climbing plants and trellises, different kinds of fruit and ornamental trees and shrubs, etc. Or go to a statuary store and be able to buy various kinds of working fountains and large statuary or vases.
Wouldn't it be fun to be able to go to an NPC fine carpentry shop and spend your gold buying large heavy tables, benches, beds, armoires? I'd love to be able to have some kind of chest or cabinet for storing bolts or folded piles of cloth in various colors. Or a linen closet that looked like it holds towels and sheets. Or an armoire that looks like it actually holds clothing! Or be able to buy from an NPC artisan various types of stained or leaded glass items? Or if some of the artist NPCs sold new kinds of artwork or stylized portraits of your characters or their pets?
It might be cool to bebe able to buy from an NPC different kinds of tack for horses, ostards, cu sidhe, hiryus, etc.
Also, maybe if we get the vendor search system, there could be another lottery for open Magincia plots, as so many of them have become empty on a lot of shards. Or for some of the Abyss housing that was never awarded or might have collapsed.
There are all kinds of decorative-type "luxury" objects that could be added and sold through NPCs that wouldn't need to affect PvP or give anyone any kind of advantage in other competitive situations but that could be a gold sink.