In my main project we added a new requirement that all new contributors meet a maintainer in a non-textual format before their first PR is merged. Seems to work well for a small project.
What an elegantly common sense solution. It's also probably a really good way to make contacts with interesting people.
Only if you have maintainers everywhere. I live in a small city in the middle of the US - how far is it to a maintainer? 4 hours to Kansas City, or fly to San Francisco? Either way the burden seems far too high.