The other heuristic I would add is one that works for commercial/closed source too: evaluate the project exactly as it is now. Do you still want to use it even if 0% of the roadmap ever materializes?

With open source, the good news is that that the version you currently have will always be available to you in perpetuity - including all the bugs, missing features, and security flaws. If you're ok with that, then the community around the thing doesn't even matter.