The only difference I can tell between SIP and something like SELinux is that SIP enforces filesystem security for any binary that isn't specifically signed by

The only difference I can tell between SIP and something like SELinux is that SIP enforces filesystem security for any binary that isn't specifically signed by Apple themselves (Which means any Apple signed programs will happily install stuff to /usr/bin), whereas on SELinux the user has a tad more control over the Access Control System, which can either be a good or bad thing depending on the situation.