Re: Another problem of a monolithic monster kernel
That is a different issue. The Linux kernel crew does not promise, in fact it aggressively denies, that internal kernel interfaces are stable. Only the user space interface is preserved.
A microkernel could have the same problem, depending on the attitudes of the implementers. They might not care about having stable interfaces between the component processes.
Personally, I think the Linux kernel should aim for some kind of stability of intra-kernel interfaces at source level, maybe breaking it only every third year or so. On the other hand, you already can use the long-term support kernel series, which already behave like that. You get breakage only when upgrading to a newer series, which you can postpone for years (https://www.kernel.org/category/releases.html).