Zdnet reports doubts about GPL licence in version 3 that will be released in one or two years. On the Debian discussion list one problem was pointed. Linux kernel is released under GPL2 with no standard option allowing to choose later GPL version instead.
I don't know how GPL 3 will look like (the project has not been released yet), so it's hard to say if there will be a think inside hat may make someone fork to use the new licence. For most project agreement of all contributors is not that hard to get, but sometimes (serveral hundred authors or more), it may be a problem.
The second thing is the note about later versions of GPL. Many projects have it (how many? I don't know). It requires trust in FSF.
The fact is that there may be a problem with contacting all the authors. Will it be a big one? We'll see. And we'll learn this way.