We've used ksplice for good amount of years (till bought by Oracle and they stopped publishing patches for other Linux distros) and all in all it was very stable technology 10 years ago

> I can't imagine a situation where I can't tolerate the downtime of a reboot but I would be willing to risk the system locking up with brain surgery gone wrong.

Because you haven't worked at that level in organization. Doing restart in some case might involve paperwork with your client and maintenance window outside of working hours even if service is redundant. And some customers are fine with a little bit of downtime and don't want active/active level of redundancy but still insist of maintenance windows for any work like that.

Live patching makes that a whole lot easier