>But once you call it an open-source project, and you have docs and a roadmap and an issues page and stuff, you're making an implicit contract with people who use it that it will do a reasonable job of solving the problem it claims to solve.

Not at all. If I do all that, maybe I just did it for practice? Maybe I get bored or RSI and quit developing software? Nobody owes you anything, regardless of what they've offered you prior.