Then, you think that the "Balkanisation menace" is only smelly FUD, and that GPLv2 and v3 can cohesist without problems ???
I'm not an expert, but we can have a GNU toolchain v3 and a Kernel v2 ???
Man I can't believe what I see. On what platform do you think the gcc, emacs, glibc, etc.. has been developed on before Linux existed?
It is a honest question.
Kernel space and user space are 2 very well separated world with very clear boundaries and public interfaces.
They aren't as clear as you might think, the "public interfaces" can be copyrightable. Many people think that using a GPLed library with a GPL incompatible program is ok, for the exact same reason, it has nothing to do with clear bounders or public interfaces, but what actually constitutes a deriviate work, and that simply means if you use some copyrightable bits.
In the case of Linux, there is a special exeption for these "public interfaces":
| NOTE! This copyright does *not* cover user programs that use | kernel services by normal system calls - this is merely considered | normal use of the kernel, and does *not* fall under the heading of | "derived work". Also note that the GPL below is copyrighted by the | Free Software Foundation, but the instance of code that it refers to | (the Linux kernel) is copyrighted by me and others who actually | wrote it.
Just like there is a specical execption for GCC/Bison/autoconf/... that allow the output to be used in/with non-free programs. For example, take a look at `(autoconf)Distributing'.
In short, just because there might be clear bounderies, and public interfaces, doesn't mean that copyright will magically vanish.