I was more thinking of stuff that is entirely mine that I just want to dump a copy of onto the web.
I don't think it's fair to make contributors assign copyright to me, especially if they are major.
I'd probably just keep a private fork from before their contributions, and, if for whatever reason my employer is GPL averse, that's their problem, and they can pay to reimplement anything they need from after that point.
Edit:
Perhaps a fair way to do it would be to say that contributors who agree to the CLA are also assigned rights to the whole code base, with the restriction of only being able to redistribute it wholesale as GPL. Similar to the way commercial sound and video clip libraries are licensed, you are allowed to redistribute it as part of another work in whatever license you like, but wholesale redistribution is only allowed under the GPL.
That would give the same advantages as a more permissive license, but reduce the freerider problem to some extent.
Re: your edit–that's an interesting idea. It seems like in practice it could be abused but in terms of your goal it's probably better to favor practicality over edge cases and a minority of people that would abuse it.
I don't think it's fair to make contributors assign copyright to me, especially if they are major.
I'd probably just keep a private fork from before their contributions, and, if for whatever reason my employer is GPL averse, that's their problem, and they can pay to reimplement anything they need from after that point.
Edit:
Perhaps a fair way to do it would be to say that contributors who agree to the CLA are also assigned rights to the whole code base, with the restriction of only being able to redistribute it wholesale as GPL. Similar to the way commercial sound and video clip libraries are licensed, you are allowed to redistribute it as part of another work in whatever license you like, but wholesale redistribution is only allowed under the GPL. That would give the same advantages as a more permissive license, but reduce the freerider problem to some extent.