Since Linux has no concept of a base system, it's a stand-alone kernel with a hodgepodge of crap around it - this distinction makes no sense on Linux.
/opt is generally for software distros for which you don't have source; only binaries. Like commercial software packages. More common on Real UNIX(R) because most Linux users outside enterprise aren't running commercial software. You're putting your $500k EDA software under /opt.
Good grief. How does this end up as the top comment on HN of all places? I'll bet anything that this author also thinks that systemd is way too opinionated and unified and that the system needs a less coupled set of init code.
Edit to be at least a tiny bit more productive: the Linux Filesystem Hierarchy Standard is about to pop the cork on its thirty second birthday. It's likely older than most of the people upvoting the post I responded to. https://en.wikipedia.org/wiki/Filesystem_Hierarchy_Standard
To wit: that's outrageous nonsense, and anyone who know anything about how a Linux distro is put together (which I thought would have included most of the readers here, but alas) would know that.