Earlier quoted context omitted.
If the project has only one main author, I would be. Even more so if they are on and off and not paid for it. Heck, TextMate and somewhat Sublime Text had such issues with 1 single dev, and those are projects that actually make them money...
That's not a fair comparison as they weren't open source so it was impossible for the community to help contribute (and the community did want to contribute when it looked like development had stalled). Where as limn is open source so if it does prove worthwhile but development stalls it would be trivially easy for any number of other developers fork the git repo and carry on the work.
It is fair, as whether it's possible for the community to contribute is a moot point if the community wont contribute.
Heck, GTK+, which is used by millions, had just one person working on it full time a few years ago (not sure if changed since), and lamenting how there's no community help in the project's blog. And that's for a hugely used and know project. I doubt a Rust UI lib would get more than that.