Totally speculative thought experiment:
It would likely depend on how much they think they'd be able to sell. I have no idea what PDS actually pays but google says the average game designer in Sweden earns ~$76K/year. Let's say there's a small team of ten, some of which will be in different roles so paid more or less (like QA, art, UX, game director, producer, etc.) and it takes them a year to develop a DLC which I think would be approximately right (if not an underestimate) especially since they're starting the team from scratch. Heirs of Alexander was $10, which was priced before all the post-covid inflation changes, but IR DLC was also priced lower than the average Paradox game because of IR's launch reputation, and this would be resuming DLC for a game that was considered shelved for years which is a risky bet. This extremely rough math suggests to break even you'd need 76K DLC sales, though that's not quite perfect as new players might buy the game or a couple of the existing DLC. And they'd most likely want to do better than break even to ensure funding for the following year of development (plus being a business with opportunity cost of IR vs some other project). I'm also totally ignoring marketing costs, currency conversion, the storefront's cut, and taxes.
So that 1.4K number is far off, right? Well, yes, but peak players is also not easily translatable into potential copies sold. Steam is tracking concurrent peak players and Paradox players are both worldwide and not necessarily daily players. We know the daily peak player count is an undercount of the actual total number of players that play the game. The only time I'm aware of where the actual data has been shared were the Vic 3 numbers released around 1.2 ("Line Goes Up" thread) which showed the total daily number of players on steam was 6x the corresponding daily peak. That multiplier is not a hard and fast rule because it varies from game to game, only counted steam players, and just because someone plays the game doesn't guarantee they'll buy the DLC. Monthly unique players would get you closer (and is likely what PDS uses internally), but that metric is not available to the public. Still, if we assume a 6x multiplier for IR and that every one of those players is dedicated enough to buy the new DLC, we currently make a ninth of that 760K budget, so a ten-person team might be too ambitious, but we've also layered on a ton of assumptions at this point that it's just a wild guess.
Let's take a different approach. Iirc, on release, Victoria 3 had around 35 people on the dev team. I believe on shareholder reports, Victoria 3 is classified as profitable (making money), but not "endless" (not making oodles of money). If IR was pulling Vic 3 numbers I think it'd be a sure bet. But maybe IR doesn't need a giant team, at least at first to save on costs, though both "smaller" studios I was going to use as an example also seem to have roughly size 30 teams (Colossal Order and
Triumph Studios). I don't have data on the profitability of AoW 4, though they do seem to still be producing DLC for it, and based on that recent spike, people seem to be buying it, so I think PDX considers it worth funding. Maybe consistent AoW 4 numbers would be okay? But if you were trying to build a year-long business plan, you wouldn't want to see IR simply cross AoW 4's lowest point, you'd want to see consistent enough demand that you think the players will still be there by the time you get your new product out.
So my completely made up guess is minimum triple current numbers over a sustained period for them to even seriously consider it. Of course, it's cheaper to assign a very tiny team of only a couple of people, but smaller team = smaller scope (or longer development time) to get anything done, which I think would make it harder to bring in new sales. The 2.0.4 patch certainly seems to have excited the existing playerbase, but would something equivalent to that size be able to raise enough funding to restart development?