I have had a few further thoughts.
Another game I play somewhat regularly is Helldivers 2. It has a cap on all the in game currencies and resources. A very simplified explination: Generally about every one or two months new cosmetics and weapons are released. To unlock these you need to spend medals. The cap on medals unlocks about 1/3 of all the new released items. You have to play the game a reasonable amout to gather enough medals to unlock the rest. This is obviously to prevent stockpiling of medals, and just buying all the new stuff right away. I assume there is a similar intention regarding the doubloon wipe and cap. I don't have much of a problem with any of this. The difference being in Helldivers, medals are obtained simply by playing the game in a normal way, so hitting the cap is relatively common and by playing a reasonable amount of time you can save towards whatever you want. Currently in SoT, some doubloons can be unlocked once per month, the rest of the time the only way to get them is by a very tedious reaper chest grind. A cap makes sense if the currency can be gathered at will.
Some more maths. I'm going to scale the current numbers up to reflect an entire season as the current season is only 2/3 of what we should get in the future
Let's make the assumption a player has all of Larina's and all of Duke's cosmetics already unlocked (I imagine this is a small percentage of people, but I am aiming for an extreme example). Also let's assume they want to buy all the new Duke item's each season. I won't take any steals into account. Feel free to add whatever number if steals you feel is reasonable
So, 3x weekenders gives 3900 doubloon. Plus 425 for the season pass. For a total of 4325. 3 new Duke item's will cost 4500. Still short. So unless you steal a huge amount (I have stolen a few, but finding people doing the voyage has been quite difficult) or exploiting with alts or other dubious methods, the cap isn't really going to affect most people.
In short, the cap isn't really doing anything as the currency is much too rare for a "normal" player. Caps makes sense when the currency is readily available. I'm happy to keep the cap, but we need a few relaible ways to generate a small amount of doubloons. Another idea I have had for this is something like 1-10 doubloons for every level of renown you generate after completing the season pass. It would keep people playing and let them do whatever they want, be that voyages, tall tales, hourglass, world events or whatever. Variety of tasks is everything, forcing endless FotDs (or other reaper chest generating activties...) is kinda dull.