If it was already published as GPL, then they cannot change that. (Otherwise they would have done so already). That's the nice thing about free software. BTW: look at the Tentacles of Evil test in http://en.wikipedia.org/wiki/Debian_Free_Software_Guideli... . We try to assume the worst. We try to assume that the copyright owners will suddenly become a second Caldera/SCO. The software must remain usage, distributable, modifiable etc. even in that case. If a software fails that test it won't make it into Debian. In fact, there are those who claim that the CDDL does not qualify because it fails exactly that test (due to the choice of venue clause).
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