I agree with the idea that if this happens, it should pretty much be a separate game.
The problem with combining this concept into one game is that it would spread resources too thinly. The type of focus that an online game would need is different than what a single player game does. I would not want a game where a lot chunk of the development energy is spent on something that I am completely uninterested in. I wouldn't buy it. Spin off the multiplayer concept for those who want it? Fine, I'm not the customer for that subject. I have nothing against them making a game like that though if there is sufficient interest.
I agree that I have no interest in micro-transactions. I came back to Sims because I like how it is not a game full of micro-transactions. It's not that I played games like that before. When Candy Crush was a huge fad among my friends, I bought a couple of lollipop hammers and then I said that it was not a concept that I was interested in and I walked away both from that game and from that style of gaming. I was turned off by the micro-transactions. I like TS's current approach which seems much more reasonable. I don't actually need extra content, if I wanted to in this game, I could ignore it. I do think it is good quality (other than bugginess, of which there is a lot but they do work on that). It's all optional and it's actually more reasonably priced than those "freemium" games.
As for my playing as a single player on my own and having to ignore or turn off chats from other players? Nope, I'm not interested. I don't want to engage with other players with my sims. I have my own game and I play on my own. I can understand people wanting their friends in their game which I might be more tolerant of than allowing random strangers to send chat notices. I would just not add any friends but I still wouldn't want multiplayer to be the focus of a PC game that I play.
Multiplayer is a different style of gameplay and story creation than single player with a different focus. I'm not even playing Sims modeled on myself. I'm not walking around as myself in the game because I can do that by going outside and living my own life. I play the game as an imaginative way to generate a world of interesting characters and plots which is something that I do myself. I'm not looking to talk to my friends in some fictitious world. I'm REALLY not looking to interact with total strangers.
A world of strangers all playing together would revolve around things that do not interest me. Seeing a total stranger walk up to fight me or "date" (euphemism) me? No. I'm completely uninterested and I would not buy that game.
If there's sufficient demand for a multiplayer game? Fine. If they want to add it to the mobile game? Also fine if mobile players want that. They don't need to mess with the existing Sims series and product for that though. As someone else said, this game requires a lot of attention for the single player format. It is also something that sets it apart from competitors.