The bus factor of Elm is pretty bad compared to more "open" projects with RFCs, a dozen or so contributors, etc. In some ways it still feels like someone's private project.
The problem with having a bus factor of 1 is that no one sees it as a problem until it becomes one.
While it seems like a bus factor of one, my understanding is that there is a plan in place (probably from the people at noredink). Even if not, the code is open source and can be forked, which should only be the very very last option.
The problem with having a bus factor of 1 is that no one sees it as a problem until it becomes one.