impossible, it wasn't. Linux was relicensed before (in 1992), it could have been again under the same reasoning, and it has even adopted some of the GPLv3 provisions not long ago.
but the Linux objection to GPLv3 was really on defending users from digital locks that render even the free portions of Linux proprietary. Linux developers were adamant that such practices should be allowed, and opposed GPLv3 on these grounds. which is weird given that even GPLv2 can be understood as not allowing this user-hostile practice. but then, Linux has never been about user freedom, as the blobs it carries to this day show.