And to assume that only the syscall ABI layer is important is quite the understatement. I have software from the 90s that would work perfectly fine if it weren

And to assume that only the syscall ABI layer is important is quite the understatement. I have software from the 90s that would work perfectly fine if it weren't for the fact that /etc/mtab is now a symlink. And that is just an example of the most smallish change -- not going to enter into the bazillions of binaries that are broken due to changes in audio APIs (even though the syscall numbers are still the same). Static linking for future-proofing/compatibility has never been a valid argument in my experience. Not only it is much easier to fix (and debug) a broken dynamically linked binary than a statically linked one, I would even dare to say that statically linked binaries break much more frequently than dynamically linked ones when you change the rest of the system. Even when you include the breakage from libraries changing under the feet of the dynamic binaries.