I have a deep, and perhaps silly, nostalgia for Morrowind. It was the second cRPG I played. The first was Neverwinter Nights, and the difference was profound. Morrowind was beautiful and first-person, even if I only got a few frames per second and maybe it's not so beautiful anymore. It was also mysterious. I knew third edition D&D, and so I knew Neverwinter Nights; even if I hadn't, it came with a thick spiral-bound manual that talked about all the classes and feats available in the game, if I recall correctly. Morrowind came with a thin manual and a big poster map covered in towns, camps, ruins labeled in a foreign script, and black Xs marking who-knows-what. It was an incomplete map, once which whets the appetite rather than satiating it. I think it was the first sandbox I ever saw.
There were a lot of things about the setting that would make it very well-suited to domain play. At the time of the game, the big volcanic island (Vvardenfell) on which it takes place is largely unsettled; for a long time it was sacred ground, then a wave of colonization occurred after the Armistice, and then a quarantine was put in place to prevent the spread of the Blight off of the island. So you've got three great houses with relatively new settlements but plenty of grudges, the old temple administration with two military orders and a waning god-king, and occupying imperial garrisons as a condition of the armistice, all mostly cut off from the mainland by policy. Plus the unfriendly ashlander natives, blight zombies, and an angry volcano god who speaks in dreams.
The player arrives into this mess on a prison ship, and the quarantine sets the limits of the sandbox. It's a clever setup.
So I sort of wonder if there's room for a Vvardenfell-alike, in the way that the Wilderlands of High Fantasy have spawned a number of derivatives. Obviously one can't just take the setting wholesale, because the wiki exists and would provide all the answers, and also because it would be unpublishable for money due to Zenimax's license. But the Elder Scrolls has a tradition of fan content, and I imagine one could give it away for free.
Outside of those difficulties, there are definitely enough verisimilitude problems to make straight-porting to ACKS tricky. Mostly the issue I think is that things were omitted and scaled down; cities have only the handful of interesting people as NPCs and few of the peasants, a smattering of farms stand in for a developed agricultural breadbasket region, and it's unclear if the distance you can travel in an in-game day is really reasonable.
So the first question for such a port would be "just how big is this sandbox anyway"? Without trusting spatial metrics, the best way to get something reasonable might be to take the vendors available in cities and use that to determine their populations, and then work from there to areas of land required to support those populations. Balmora, for example, has four smiths, four inns, and one bookseller, which would be consistent with a population in the 6500-8000 range, which in ACKS would be a large town or a small city, class IV market. This seems roughly consistent with the feeling of the place, though it's billed as the seat of a great house. Vivec has six smiths, which would put it around 9000 people, but two booksellers, suggesting a population of closer to 13000, just sneaking into City status with a class III market. If I count alchemists and enchanters as "magic shops", then I get much bigger numbers; Vivec has 8 alchemists and four enchanters, suggesting a population north of 33000 and Large City / class II market status, while Balmora has 2 enchanters and 3 alchemists, for 14000 and City / class III market. Not counting apothecaries (which I assume are mostly healers rather than selling ingredients to wizards), Sadrith Mora (another house seat) has 4 alchemists and 2 enchanters, for 16800 population and class III. Ald'ruhn, the final house seat, has three enchanters, three alchemists, three smiths, and one inn, so population ranges from 4500 to 16800, against class III or IV.
Taking either of these configurations, class II Vivec and class III house seats or class III Vivec and class IV house seats, we end up on one of two rows of the Urban Population table, where Vvardenfell has somewhere between 625,000 and 2.5 million inhabitants. This is incongruous with the fact that Duke Dren is only a duke, as those are prince-to-king numbers. Taking this map, which has Vvardenfell looking like about a third of the area of the province of Morrowind, and knowing that the province of Morrowind as a whole is a kingdom, principality-tier population seems reasonable. So let's go with the lower, principality end of those population figures. The duke is sort of a puppet anyway. This also means we're basically writing off the extraordinarily high wizard-merchants-per-capita and going with the population numbers from smiths, inns, and booksellers. Maybe we can bring the wizards back when we get to per-class demographics; certainly Telvanni settlements seem to have more wizards than clerics or thieves.
Getting back to distance, we need to first traverse population density. Large parts of the island are wilderness or borderlands. Given that the island is newly settled, and that they were defeated in war by a Rome-analog power, something in the lower end of the population density range is probably reasonable as an average. There are dense agrarian regions with large enslaved lizardman and catman populations, but then there are also low-density pastoral regions. Taking a population of 625,000 (or 125,000 families) and 250 families per settled hex on average, we get 500 settled 6-mile hexes, or 31 settled 24-mile hexes. Taking the unsettled interior as about one and a half times as large as the settled coasts, we need another 45 24-mile hexes in there, for a total of around 80 24-mile hexes, or about 9x9 grid (call it 11x11 with some water). As a nice bonus, this is right around the recommended size for a detailed region in ACKS, and it should give me enough six-mile hexes of wilderness to actually make rooms out of.
"Beyond the Ghostfence, there are no safe places, no
allies. Stockpile resources. Plan for retreat and replenishment."