There was a discussion in discord lately about the thief's "class fantasy". The wizard's class fantasy is fireball at low levels and doing mad science at high levels. The fighter's class fantasy is cleaving through a bunch of dudes at low levels, and leading armies in triumphant mass combat at high levels.
One option for the thief's high-level class fantasy is being a crime lord, having goons kiss the ring on your finger, planting horse-heads, etc. Well and good, but complicated.
But an alternative possibility for the thief's domain game could look more like this:
And then your aim as a thief is to just accumulate and protect an enormous amount of wealth. Maybe give bonus XP for the value of money permanently allocated to your hoard, like fighters get XP for the money they spend on their fortresses. And like losing a fortress, if your treasure gets stolen, you lose the XP. Maybe HP too - it causes you physical pain to spend from your stash.
(Or maybe take the hoard value, divide it by 30, subtract your domain income threshold, and that's your monthly earned hoard XP)
I like this because it ties into the whole "buried treasure" folklore - Captain Flint's treasure in Treasure Island, the gold in the cave in Tom Sawyer, the cache in The Good, The Bad, and The Ugly. I like that it mirrors actual play that we saw during the first ACKS game, where players didn't trust each other much and would go out in the desert alone to bury their gold and only tell their most-trusted henchmen where it was. Incentivizing accumulating and keeping safe vast quantities of gold shifts the thief's domain game to be more like the wizard's - suddenly he has good reason to build a dungeon full of death-traps. Or multiple dungeons, because decoys.
Parallel to the domain random encounter system, have a check every month based on the thief's hoard value to determine if some treasure-hunters have gotten the right location and make an attempt on it.
I'm not sure what the role of hijinks would be in this model. I like the idea of having hijinks just do stuff in the world that you can use to make money, but that doesn't just make money directly. Treasure-hunting is perfect as-is; stealing and smuggling are both workable, with the addition that you can't sell stolen goods in the market that they were stolen from (or they'd be recognized), and smuggling just lets you avoid tariffs. I like the idea of tying spying and carousing into clocks on settlements, where spying lets you know the state of a secret clock and carousing or rumor-hunting or whatever it was called tells you the existence of a secret clock. But I could see the numbers not working out with having standing / long-term guild payrolls, if the profit margins go down. Maybe a better way to think of it is that you have certain people that you know who owe you favors that you can call upon to do jobs for you (and then their share and how well it goes determines whether they'll work for you again).
(It always struck me as awkward that you could just hire thieves. Someone who just pays thieves makes himself a mark for later - there must be more money where that came from)
Depending on hijinks changes, this would probably change the thief's domain game from being mostly a cash-source for the rest of the party to being a cash-sink, like all/almost all of the other class' domain-games.
A couple of wilder extensions:
Dwarves also build vaults. Dwarves also sort of have some thief value mechanics. Maybe dwarves should get bonus XP for socking away gold too.
Venturers too, obviously.
If a character who sequestered gold into a hoard for XP purposes dies, and the is gold stolen after his death, he might rise as an undead of XP value equal to his XP in life (including the value of the stolen gold). If you kill it, then you have earned that XP and the sequestered gold isn't double-counted; it now counts as recovered again.
Magic items - does their value count towards hoard value? This seems like it could get really inflationary, but might also be a good "magic sword sink". Maybe you can only count magic items up to the value of gems and coinage.
Apotheosis - you know who else besides dwarves accumulates treasure hoards? Dragons. Maybe gold corrupts. Maybe if you accumulate enough gold and hide it away where only you know about it, it starts to change you. Maybe dragons are the end-state of high-level thieves who take naps in their treasure rooms and wake up with gold sticking to their skin like scales, and with an insatiable fire in their bellies to accumulate more wealth. Maybe this is a good explanation for having no dragons of less than 9HD, if that's when the transformation can first begin.
Obviously, this also explains why there is a dragon in the dungeon - he built it to protect his treasure, when he was just a man.
If gold has supernatural weight, could gold also be an explanation for making thief abilities supernatural? Could you burn hoard value to power special abilities in the dungeon, turning glittering gold pieces whose luster only you know into tarnished coppers and expending that glamour to cloud the minds of observers, to distract, to disguise?
If you have a supernatural bond to your hoard, and you have magic items in your hoard... can you use that link somehow?