@raccoonformality if a timed release appeals to you, have a look at Oni2's model (before the maintainer abandoned the project): source available, but any git commit will only become open source licensed 18 months later.

The interesting thing about that is that it doesn't necessarily discourage contributions, because you know it'll eventually be open source anyway, but the creator gets to monetise their product as long as they actively maintain it (and stay ahead of the timed license).