So, you could start to incorporate GPLv2-or-later code. But you could only do it in code that you could clearly identify as your own original code, and not a "derivative work," because derivative works need to follow the same license. So you'd basically be adding new files under GPLv2-or-later, there'd have to be a boundary between old files and new files where you can't ever move anything from one to the other, until eventually everything is rewritten and the old files can be deleted.

Except... when on earth would everything be rewritten across that boundary? If I'm coming in with a one-line fix to an existing function, I can either submit my one-line fix, or I can come up with a completely new function written from scratch, without looking at the original one (or at least different enough that no one could accuse me of doing that), all just so that maybe in a few decades the kernel can change licenses.

If you force the issue and just refuse to accept patches to any v2-only code, then the cost of maintenance goes up exponentially. If the current Linux maintainers did that, I have to imagine they'd lose to a fork that didn't do that. The fork would be quicker to develop, and would have all the corporate contributors that make up the overwhelming majority of kernel dev these days.

And that assumes everything will naturally be rewritten eventually. Yes, there's a lot of churn, but not everything changes. Take a look at fs/ext2/file.c, for example -- you'll find a mix of changes from earlier this year, changes from ten years ago, and changes from almost 20 years ago. (Before you ask, ext4 isn't really better.)It's hard to see why anyone would bother rewriting the ext2_file_operations struct from scratch, or what that would even mean -- aren't you building a brand-new filesystem at that point?

You'd have a better chance of rewriting it all in rust. I'm serious! Rewriting one file at a time in Rust (or adding new stuff in Rust) can actually give you improvements over C right now, today. Relicensing one file at a time as "or later" doesn't give you any of the benefits of GPLv3 until the entire kernel migrates.

And then I'm left wondering: What benefits? It's already painful to try to get projects like Android to upstream their best changes. It's not like taking the kernel GPLv3 will force vendors to unlock all bootloaders. It'll just force them to stay on their v2-only fork, or switch to one of the BSDs. It's hard to see either of those options as a victory for either Linux or software freedom.