So, after checking the Jenkins site and the community, we have decided to write a new plugin, as nothing out there (or currently in the works) will do whatever it is we want; where do we start?
We could start off with a new blank Eclipse project and write everything ourselves if we really wanted to, but that would take ages.
We could use the skeleton Hello World project, delete what is in there, and start adding our code to that, but this doesn't sound like the sort of approach we'd expect to follow, given all the code reuse and avoidance of duplication we've been talking about for a while now.
Even if you have a completely novel idea for a plugin, there is bound to be something roughly related to it out there already; even if this doesn't provide the functionality that we want, it may work in a similar way or use many of the same extension points that we have identified as being of interest to us, so it's worth checking this out.