That's what contributory license agreements are for: any project that plans to follow such a route needs to get all their developers to sign one in order to get the rights.
In my experience this was some effort, but not overwhelmingly so, IMO. This would probably be more difficult for a larger project, but other projects have done similar things (e.g. VLC's planned relicensing of libVLC to LGPL).
In my experience this was some effort, but not overwhelmingly so, IMO. This would probably be more difficult for a larger project, but other projects have done similar things (e.g. VLC's planned relicensing of libVLC to LGPL).