Back around 95/96 I once untarred a etc directory from a Slackware install over a redhat etc directory. It booted and worked perfectly. It was really hard to update though. Redhat started out as Slackware.
I keep one machine with slackware installed. I use it for various purposes include light desktop use. I occasionally compile a kernel. Just to keep the skill. My daily drivers are Debian and Ubuntu machines though. These pretentious new users(arch, cough, cough) probably wish they had the patience to keep a Slackware installation going full time.