I've only looked at ubuntu but it seems like it's maintained at least there. It looks like mint 15 which dw says is the most popular distro seems to use it.
And I think your predictions sound a little dire. I'm no expert but systemd does seem to be a very active project, which made me concerned, but their external interfaces are fairly stable. That leads me to hope that maintaining a shim will require a lot less effort than it could in a scenario like the one you suggest. If upstream wants to pass the torch and someone takes it up that's great. If upstream just drops the project, then, well, that's a problem for ~14k debian users and a lot more users from other distros. One thing I'd like to do is reach out to sysd-shim maintainers in other distros. But, in the end, sysd-shim seems to be a fairly recent release. I'd like to try to nurse it along for the next couple of months and see how things go. I personally don't have any plans right now to take over upstream, but maybe that will change if I get more familiar with the code.
