The Prof-UIS license does not apply to plugins or the runtime because they do not use any Prof-UIS code at all.
As for the idea - well, yes, this is how open source projects are meant to work, so anyone can code and contribute - I would encourage it more, but I'm afraid I just don't have much time these days. It is a good idea. It would be very useful to have people debugging the code to point the devs to particular lines of code that are at fault, or even just reviewing code to hunt down potential problems. However, most of the code in Construct right now is pretty messy and overall badly organised, so I would prefer to wait until Construct 2 to take a more structured, organised approach to these "development technician" roles. (it might also be nice for people relatively new to coding to get project experience)
As for how this kind of project would really work, I see it a bit more like this. Changing code in a project with 100,000+ lines of code can be very difficult and have unexpected repercussions, even for the original developers! So a role of reviewing code for potential (or actual) problems, since a second pair of eyes can really help, debugging code relating to currently open bugs and finding the problems in the code, and writing patches for plugins, would be useful. Maybe we could also give some people developer access to the SVN and see how "third party" patches go. But given my experience on Construct 0.x, lax coding standards can really cause big headaches later on, so I would be very strict and picky and would probably reject code submissions outright if they don't comply exactly. This might seem harsh, but an open bug you've had your eye on might have been closed by now if we'd been stricter on this ourselves in 0.x.
Anyways, it's an interesting discussion (sorry I arrived late). Any thoughts on that?