Disregarding all the banter about what "open source" means -there are separate issues at hand.
One is the actual license terms the older versions were distributed under. Those matter.
Another is how the project itself was run, specifically how copyright assignment worked. If contributors were required to assign copyright to the project maintainer (or whatever) in order to commit to his main branch, as is the case with many projects, then he can likely do whatever he wants in terms of re-licensing. If that wasn't addressed clearly, there might be wiggle room for closing it off - contributors may have some kind of copyright claim if their work was taken and used under terms they didn't agree to.
Another is PR - that one is obvious.
As for the "Open source means you give back" - let's get over it - that's not what it was originally about - you have no "duty" to contribute - it's just a fantastic, common side effect that lots of people like to take advantage of.
End of story - if you are contributing code to someone elses project, be sure you understand where you sit in terms of copyright.
One is the actual license terms the older versions were distributed under. Those matter.
Another is how the project itself was run, specifically how copyright assignment worked. If contributors were required to assign copyright to the project maintainer (or whatever) in order to commit to his main branch, as is the case with many projects, then he can likely do whatever he wants in terms of re-licensing. If that wasn't addressed clearly, there might be wiggle room for closing it off - contributors may have some kind of copyright claim if their work was taken and used under terms they didn't agree to.
Another is PR - that one is obvious.
As for the "Open source means you give back" - let's get over it - that's not what it was originally about - you have no "duty" to contribute - it's just a fantastic, common side effect that lots of people like to take advantage of.
End of story - if you are contributing code to someone elses project, be sure you understand where you sit in terms of copyright.