The FHS thing in Debian and Ubuntu must be relatively new, I certainly have no recollection of it back then when we looked into delivering unbundled software for it. And we did look for it, and we even combed through the Debian packaging specification back then.

Whatever it might be, or has been, if Debian and Ubuntu did get /opt, /etc/opt, and /var/opt and are now one small step closer to being System V compliant (from which FHS stems), I for one am very glad for that.