Linus has the (imho: valid) expectation that kernel changes should not break userspace (for detailed explanation see: https://unix.stackexchange.com/a/235532). Even if the version numbering is not an explicit API like say, file system drivers, the versioning of the kernel is an implicit guarantee that the kernel has made to userspace.

At some point, I think so.

It's similar to a discussion I saw on here about Chrome adding a feature that you could use with a certain html attribute iirc, ie <div newattribute> or something.

Supposedly, nobody should have an attribute called 'newattribute' anywhere in their application, but that doesn't mean that there are is a non-zero amount of applications out there that do.

The problem is not so much that you can point and laugh at the crappy regexes, or crappy html-devs, the problem is that some scripts on some server, or some sites somewhere don't really have a maintainer anymore.

For tiny, tiny projects, you don't really have to take this into account, but if you're Chrome or the Linux kernel, you definitely should take it into account.

Now double that estimate, add some padding, and I am looking forward to the release of 2230.1

spoken like a true project manager