There is no such decision to be made. Linux has a "GPLv2 only license" and every contributor owns the copyright to their contribution. It's not possible to switch Linux to GPLv3 even if they want it.
It's not easy, but it's possible. You just take written permissions from everyone who wants to give them, and if there are significant bits uncovered, you rewrite the code. That's how it could be done. Unfortunately if the majority of the important contributors do not want to change the licence, it won't be possible to do this.
--David.