Long term it might be better to get some existing organizations involved in some of these niche use cases. There are non profits out there operating in different industries and they would have the momentum and support to keep instances going, as opposed to a single person running an instance locally.

For the general purpose instances I don't feel as bad (it sucks, but there's more out there). For the topic based ones, it's harder to migrate those communities to something else and it's not great to have everything on one instance