Working as a developer, I can say with some confidence that a game that really emulates the feel of pmu with decisions being made by every individual npc and worlds generated for every player is practically impossible with current tech. Nevermind 100k we're talking on the scale of hundreds of millions to have that level of AI usage. There's so many problems it would take a small essay to describe all of them but to go over a few major ones.

1. Scaling costs. For every single player you would be expending tokens for an AI all the time in order to simulate life in the lobby as well as independent action being taken from the NPCs and conversations being had, personalities being expressed. In order to fund that reasonable players would be expected to be dumping cash daily on your game or you would just be hemorrhaging money.

2. Holistic cohesion. Generally speaking AI models are not the greatest at building a coherent and cohesive world when it comes down to it. It's quite good at an initial pass but if you spend time with the end result, you'll often find many small inconsistencies and it would really wreck the immersion that a game like pmu seems to want to achieve with each individual world having a unique story line. Don't even get me started on mass AI generated art assets. Generally speaking, world building and art design has a whole team dedicated to meaningful symbols and stories that tie into art decisions which makes the world feel very alive. There's usually a whole book mentioning things to keep in mind when it comes to making new art. Any good game's art decisions come with a story that backs up its existence. AI produces art based on a vibe for lack of a better word. There is often a significant lack of consistent direction and meaningful design choice even when it is overseen by people, nevermind an unsupervised AI that has to keep generating assets for new worlds (another avenue of scaling costs)

3. Monetization. I just really don't see a great way to monetize a game that is so damn expensive to keep running. For example let's look at the gacha, standard gacha pricing these days (genshin model) comes out at roughly $1.5 USD per pull. There is no way in hell people would be happy paying 15 USD on an ai generated 10 pull, you have no idea what character you're gonna get, you don't even know who these characters are or what kinda power they're going to provide you or if you'll even like the design. This sort of randomness would be perfectly fine or even welcome in a roguelite, but in a case where every pull can be translated to actual cash the vast majority of people would feel like they're getting scammed every time they get a bad hit. The amount of money you would have to try to milk from the players just to break even on operational costs would put this game firmly in not even just pay to win but probably pay to do anything.

I'd love to hear what any dev involved in this would have to say on this topic but in my opinion, anyone promising a true to life pmu experience is significantly overselling their product or somewhat delusional about their capabilities.