Besides the Mir-WM from Canonical, there are plenty of in-the-wild examples of projects that are GPL, but in which the central-author retains control of the source, to relicense as they please.
Folks above have already mentioned OpenOffice, which got forked into LibreOffice shortly after Oracle bought out Sun, and is now currently IBM+Oracle ApacheOffice with a BSD-style license (so that someday IBM+Oracle can offer their own downstream proprietary derivatives of same) versus LibreOffice which has less typically-corporate backing but gets support from the distros.
Probably more important is the OpenJDK versus OracleJava and GoogleJava situation (both the latter two maintain private repos for Java-on-windows and Java-ported-to-android respectively).
Qt was mentioned, and KDE+GPL versus proprietary release.
Another example with less political baggage might help clarify the span of such things: TightVNC, from Estonia (if memory serves), uses the GPL throughout, but explicitly offers to relicense the project for proprietary projects that want to pay for the code without paying for the GPL. They are not the biggest VNC fish in the pond, and there are plenty of GPL-all-the-time VNC projects, but TightVNC has still survived (even against RedHat's own TigerVNC) for quite a long time now. The project is also good code; I use it.
So, although I'm definitely wary of the Canonical distro turning into the equivalent of TiVo, or the mini-equivalent of Oracle-nee-Sun... what they're doing is not actually wrong in any way, and might turn out for the better. For instance, look forward to three or four years from now, when Google has half the phone market, with their BSD-style preference and their willingness to let phone-and-carrier-folks lock down the bootloader. If the other half of the market is win9 and iOS, that is no good. I'd rather the other half of the market be Canonical with their GPL3, and have the then-in-the-future-backers of Canonical present their new terms to the phone-n-carrier folks, namely, time for GPL3, so we can keep google's spyware and lockdown tactics from beating us.
Yes, this could be a pipe-dream. Maybe the folks at canonical will turn out to be like the folks at google. (Or maybe it will turn out that google folks are the ones who pressure the phone-n-carrier industry to open up... I'd love to be surprised that way. Owning moto gives google the advantage of being able to produce open hardware, not just open software, if they could just bring themselves to decide to do so.)
In the short run, I'm reasonably worried about the Linux fragmentation that mir/wayland/surfaceflinger/x11 are about to cause. I'm *very* worried that wayland will follow mir, in happily working with binary-blob graphics drivers. (See the mir homepage which is careful to mention several times how it will 'function' with the existing open-source drivers but emphasize that mir will be 'optimal' with proprietary nvidia slash amd drivers on the desktop and proprietary android-like drivers on tablets and phones.)
But in the long run, GPL3 is a pretty good constraint, even with the CLA. It mostly depends on the sort of people that are in charge of Canonical, a few years from now. If you want to have an impact on what licensing constraints the UbuntuPhone2017 will ship with, prolly it is better to try and get some power over decision-making at that point. Ubuntu has no stock, since they are private, but if they do try to become a phone-power they'll probably go public. Better to have GPL-friendly folks on the board, rather than folks like Steve Ballmer, right? Also, better to have some GPL-friendly folks on the Ubuntu Tech Board where MJG used to reside, and working on Mir.
Am I suggesting that everybody just trust canonical, or that everybody just buy ubuntu Inc stock, or even that everybody contribute to mir? Nah. I'm just pointing out that it is better to wait and see, than to harshly judge now. Maybe our suspicions will turn out wrong. It's fine to voice the suspicion, by the way. If we don't publicize the risks to freedom, nobody will be aware there even is such a risk, after all. But the Mir project is not yet proven to be a risk to freedom (and Wayland is not yet proven to be a panacea for freedom -- look at the proprietary firmware stuff collabora did with the wayland backend for the raspberry pi).
I guess I'm trying to say this old chestnut: trust, but verify.
Other projects with central-author-relicenses-as-they-please
Folks above have already mentioned OpenOffice, which got forked into LibreOffice shortly after Oracle bought out Sun, and is now currently IBM+Oracle ApacheOffice with a BSD-style license (so that someday IBM+Oracle can offer their own downstream proprietary derivatives of same) versus LibreOffice which has less typically-corporate backing but gets support from the distros.
Probably more important is the OpenJDK versus OracleJava and GoogleJava situation (both the latter two maintain private repos for Java-on-windows and Java-ported-to-android respectively).
Qt was mentioned, and KDE+GPL versus proprietary release.
Another example with less political baggage might help clarify the span of such things: TightVNC, from Estonia (if memory serves), uses the GPL throughout, but explicitly offers to relicense the project for proprietary projects that want to pay for the code without paying for the GPL. They are not the biggest VNC fish in the pond, and there are plenty of GPL-all-the-time VNC projects, but TightVNC has still survived (even against RedHat's own TigerVNC) for quite a long time now. The project is also good code; I use it.
So, although I'm definitely wary of the Canonical distro turning into the equivalent of TiVo, or the mini-equivalent of Oracle-nee-Sun... what they're doing is not actually wrong in any way, and might turn out for the better. For instance, look forward to three or four years from now, when Google has half the phone market, with their BSD-style preference and their willingness to let phone-and-carrier-folks lock down the bootloader. If the other half of the market is win9 and iOS, that is no good. I'd rather the other half of the market be Canonical with their GPL3, and have the then-in-the-future-backers of Canonical present their new terms to the phone-n-carrier folks, namely, time for GPL3, so we can keep google's spyware and lockdown tactics from beating us.
Yes, this could be a pipe-dream. Maybe the folks at canonical will turn out to be like the folks at google. (Or maybe it will turn out that google folks are the ones who pressure the phone-n-carrier industry to open up... I'd love to be surprised that way. Owning moto gives google the advantage of being able to produce open hardware, not just open software, if they could just bring themselves to decide to do so.)
In the short run, I'm reasonably worried about the Linux fragmentation that mir/wayland/surfaceflinger/x11 are about to cause. I'm *very* worried that wayland will follow mir, in happily working with binary-blob graphics drivers. (See the mir homepage which is careful to mention several times how it will 'function' with the existing open-source drivers but emphasize that mir will be 'optimal' with proprietary nvidia slash amd drivers on the desktop and proprietary android-like drivers on tablets and phones.)
But in the long run, GPL3 is a pretty good constraint, even with the CLA. It mostly depends on the sort of people that are in charge of Canonical, a few years from now. If you want to have an impact on what licensing constraints the UbuntuPhone2017 will ship with, prolly it is better to try and get some power over decision-making at that point. Ubuntu has no stock, since they are private, but if they do try to become a phone-power they'll probably go public. Better to have GPL-friendly folks on the board, rather than folks like Steve Ballmer, right? Also, better to have some GPL-friendly folks on the Ubuntu Tech Board where MJG used to reside, and working on Mir.
Am I suggesting that everybody just trust canonical, or that everybody just buy ubuntu Inc stock, or even that everybody contribute to mir? Nah. I'm just pointing out that it is better to wait and see, than to harshly judge now. Maybe our suspicions will turn out wrong. It's fine to voice the suspicion, by the way. If we don't publicize the risks to freedom, nobody will be aware there even is such a risk, after all. But the Mir project is not yet proven to be a risk to freedom (and Wayland is not yet proven to be a panacea for freedom -- look at the proprietary firmware stuff collabora did with the wayland backend for the raspberry pi).
I guess I'm trying to say this old chestnut: trust, but verify.