Just throwing stuff at the wall here, but with the coming population collapse, I'm thinking we might be able to derive some lessons or maybe even a blueprint for how to navigate said collapse by examining MMORPG economies. I know that in the past economists have studied WoW in earnest so maybe there's still some insights yet to be mined.
How does the economy change once the server population starts shrinking?
I know from my own experience playing FFXI back in the early 2010s that there were regularly specialized materials on the auction house that wouldn't get stocked regularly. In my case it was some fish and for a couple weeks I was able to make good money at it because while there was almost no one supplying the item there was definitely still a demand for it. Then someone started flooding the market and I moved on to other ventures. No idea if the end result of that was a temporary supply or if it turned into a stable availability of the product. Maybe the one guy just made a whole bunch of product the one time and then once it was sold he moved on to the next thing and all the smaller producers like me ended up gone and the product itself just outright vanished from the market.
I imagine the dynamic is quite different now as the population dwindles further, although they do consolidate servers so that might throw a wrench in the fact finding opportunities here.
MMOs being entirely artificial can just cheat and add resources as needed.
The Homecoming server group for City of Heroes always knew they were never going to have the same numbers the retail servers did so took steps to both support and avoid certain previous market issues.
Back on retail the materials known as Salvage which were used to create the equivalent of gear and cosmetics were only ever supplied by the players. There were 3 brackets that ranged from level 4 up to 50. These brackets were 4-25, 20-39, and 35-50. Understandably the highest bracket was one of the easiest to farm in general but also because actual dedicated farm builds functioned at level 50 so simply meant significantly more time invested in sourcing drops.
This again understandably led to lower bracket drops being less available and culminated in one or two specific low level drops, Luck Charms and something else, being bought out by one player and re-listed at several magnitudes greater in price.
This itself is just how markets can work, low supply and high demand can lead to price gouging and what limited stocks being available getting manipulated.
What Homecoming did to avoid this was change how the game auction house classified salvage so that ALL salvage was fungible within its respective category. All common/white salvage was considered the same, so if someone was selling a bracket 3 Spirit Thorn it could technically be sold as a bracket 1 Luck Charm when someone else specifically bought that instead of the actual item listed. This was the same for uncommon/yellow salvage, and rare/orange salvage.
What this ended up meaning was that level 50 farmers could in theory perpetually supply the AH with everything since all the bracket 3 drops they got could just as easily translate into bracket 1 or bracket 2 items depending on what others were buying. This helped solve potential supply issues, and because setting up a farm build was relatively easy many players had one and would simply bulk dump anything they got for as low as possible which then kept prices down.
What Homecoming also did was set up the AH to always have its own seeded infinite supply of items at set prices, albeit prices players would rarely ever reach unless things got weird, which they did a few times.
You would rarely, if ever, find a player spending 100k on yellow salvage because player supply was so great everyone kept undercutting each other. But just in case that player supply ran low for whatever reason there was the 100k line which meant you never had to spend more than that for what you wanted. Some still would because they didn't know this was how things were set up, and others simply didn't care because earning currency with a farmer was not only extremely easy but something you could quite literally do passively by AFKing said farm build in a map and either going to do something else or even just going to sleep.
Homecoming didn't mind players doing this, they knew farmers were helping supply the server with cheaper alternatives than the seeded items, in addition to things that weren't seeded like the very rare/purple drops. Players complained about farmers but in the end they were more advantageous than otherwise, many simply didn't want to do it themselves and didn't want others to have the option to either.
This sort of thing only really happens on private servers and small ones at that which aren't still looking for other means to milk players for money. A lot of WoW servers still have various p2w options on their own 3rd party shops which range from cosmetics to gear to profession perks that cause problems, so it depends a lot of the time on which game, which server group, and which devs you end up with whether there are attempts to improve QoL of whether it's simply just another cash revenue scam being attempted.
Either way, games too easily break the rules for economies since they can quite literally print money with the press of a button, but also print services and rewards which distinguishes them from how IRL money printing works. We're not yet at the point you can simply press a button and have an F-22 Raptor ready to go infront of someone.
Having played HC for some years I'll add the only real limit the devs imposed on farmers was having no more than 3 characters logged in at a time. Players could easily manage this by running multiple clients at once and barring special circumstances like open world raids, where players were usually limited to just 1 character/account unless on a low pop server that wouldn't reach the 50 player zone cap, the only thing stopping anyone from running 3 farmers at the same time was their own motivation and time to organise it all. Plus the point doing so meant they couldn't then actually play the game at the same time due to the 3 character limit.
Still, it was extremely helpful having farmers dumping so much into the economy because they not only earned the item drops but also generated currency while doing it. The AH would always take a cut which removed currency from the game. So those who "made" money through flipping and reselling were really only redistributing currency while also removing some per transaction. Farmers on the other hand would often generate so much they'd spend just as much on things they wanted because they had millions, if not billions, and didn't care how much they spent, so sometimes poorer players would get far more for their sale than expected.
Also at times sometimes people fucked up and put an extra 0 or even a 9, which is how I had items I usually sold for 10 mil sometimes earning me 100 mil if not more.