Lootboxes and Crates + Keys system is just gambling, not even related to FOMO. Which both suck by the way.
While I understand that the money that goes from these cosmetics, go back into the play-fund for the games, the whole economics in the game in the development as early as it is, feels just wrong, as it immediately sets the standart for incoming games to aim for the money and not for the passion of development that a lot of people came for in the games like GMod in the first place.
Economics and games just don't mix well and it starts making a corporate hell like Roblox is, where slop is made just with the aim of getting on the front page. I have incredibly high faith in S&Box as essentially an engine that allows to both publish games on it's platform and let people who enjoy this platform play them AND allow developers to export their game for stores outside, that all is honestly truly awesome. But this weird feeling of concern for the game standing so aggressively on making actual FOMO cosmetics, which you can only get for a normal price when they launch and then it's just the marketplace folks gauging prices, make it feel pretty icky.
I honestly don't know any other idea for a reliable way to make money for the play-fund, so I guess we have to settle for this, but it still just doesn't feel so good, as well as the explanation for it feels a little too aggressive, when you could have explained in a simpler, calmer way that you need this money to fund more games.