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xyz Imho, it ought to be a commercial game.
If a person wants to play but doesn't want to pay, they will almost always find a way. If the game will be in demand genre (The Sims 4 Hits 10 Million Active Users), we can expect a significant influx of funds simply by statistics.
There is an example of a completely free and successful game. Unfortunately - NSFW.
390
Paid members$1,419
Per month
In my opinion for one developer — very not bad.
Megalomaniak Few that would likely sympathize with the goal of funding the underlying engine itself.
I don't see that as a problem. How to divide the received funds is the concern of those who received them — the game developers. In my project I would divide the funding into two streams: funding only the game and share with the developers of tools (game engine, 3D-modeling software, etc.).
xyz Producing a good looking commercial game
Good looking — I agree, but why commercial?
If you accept the idea of creating a sims-like game, I can imagine the way of its advertising and distribution. I'm tight with the sims community. I'm even a moderator on a local fan site.