"IIRC, some contributions are v2 or later, but as long as a majority of the code is v2 only, the whole package is v2."
If even one component is v2 rather than "v2 or later", then (I'd assume) the whole project is v2-only, majority or no. It's also not clear if it's permissible to make contributions under "v2 or later" licensing terms, since those contributions are derivative works of Linux itself (which is v2-only).
This will almost certainly always be the case, since changing Linux's license to "GPLv2 or later" (let alone GPLv3) would require unanimous consent from every contributor (and seeing as how - IIRC - one or more said contributors are dead, that consent is thus impossible to achieve unanimously).
The only sensible way to do it is to locate all parts still licensed under GPLv2 and ask every copyright owner alive (or their estates) to relicense their contributions under GPLv2+ or rewrite them from scratch licensing them under GPLv2+.
And convincing Linus the rewritten versions are objectively better than the old ones.
If even one component is v2 rather than "v2 or later", then (I'd assume) the whole project is v2-only, majority or no. It's also not clear if it's permissible to make contributions under "v2 or later" licensing terms, since those contributions are derivative works of Linux itself (which is v2-only).
This will almost certainly always be the case, since changing Linux's license to "GPLv2 or later" (let alone GPLv3) would require unanimous consent from every contributor (and seeing as how - IIRC - one or more said contributors are dead, that consent is thus impossible to achieve unanimously).