Does it need to be objective though? I think a vague list of criteria including "The project must benefit a community", or "The project must not be made solely for the benefit of their employer", and have someone review the proposal should be enough.

??? seems straightforward... among other things, require the applicant to do the work / provide evidence...

Some government team could just make a list of allowable projects, updating it every year, and starting for example with all projects with over 100 GitHub stars or some similar metric.