Not so much stability issues, you would just run out of everything - CPU, RAM, you name it. The game is still quite demanding. But technically, it should be possible. Most, if not all, of the tech should be there.
As @Teleros says, map segments won’t really work because you would violate time. If you split your village in half and play with one side for a year and then merge them back, the other side would miss a whole year of stuff happening.
SimCity 4’s map/region system is just a glorified savegame. Whenever you load one city, it quickly reads the surrounding map files to adjust demand/offer of the trading goods - that’s it. After that, nothing is simulated. That’s the reason why you can build two cities adjacent to each other, one habiting millions of Sims, exporting thousands of tons of garbage - right to a village of 45 people, with one single trash deposit. It’s not even really cross-validated.
Personal thought: By having this distinct enough, like SimCity 2013 does, it suddenly becomes a lot more possible… ish. The time problem persists, but you could solve that by playing carefully. One possible approach that I would do to solve this issue would be some sort of… forced colonisation. You can take some goods and citizens, move to another map, and then play there for, say, a year or so. After that, you take weekly turns in your colonies/home country, to make sure time and stuff spreads evenly. Goods, and units, could be traded between these settlements more or less freely. It’s something that has been on my mind for some time. Maybe I’ll do it once.
Bigger maps won’t work, or at least, didn’t work back then. I think you could at most make maps twice the size before you ran into memory issues - that was before the 64bit client was released. But bigger maps mean more terrain, more possible pathfinding, more everything.
And please, stop with the code formatting (i.e. stop putting four whitespaces in front of your paragraphs). It’s making me a bit itchy.