If the goal is to get new players to join the game because half of the leagues are empty, creating a subreddit in Reddit would do wonders, in my opinion.

Some other GM games have them, and it's great to see the communities they have created. Here's an example (not spam, I just enjoy the game and the community is great there): https://www.reddit.com/r/BasketballGM/

People post about their own teams/players, give advice...

I understand it's a bit redundant if there's already forums here in MFN, and I don't know if jdb would allow it/if he's against it, but I think it would bring new players to the game.

I guess there's some cons to bring new people this way, but it's sad to see owners leave MFN every day... what do you think?

well, start one.