It would be kinda nice if the default group owner of /usr/src/linux* would be a separate group, and if sub-files would be g+w and sub-directories would be g+ws.
This would allow any regular user in that group to build a system kernel without switching to superuser.
Reproducible: Didn't try
Steps to Reproduce:
Erm, you still need superuser to boot and to install modules into /lib/modules/...
My suggested solution to building kernels as non-root is to go the KBUILD_OUTPUT route.
Since this would fully satisfy your request, without having to change perms I shall close this bug invalid.
Although this document is now invalid..
I would point you to section 3