Here at The Reg FOSS desk, we've felt this was coming ever since we reported that Big Blue was launching new POWER servers which didn't support AIX – already nearly eight years ago. Even if it was visibly coming over the horizon, this is a significant event: AIX is the last proprietary Unix which was in active development, and constitutes four of the 10 entries in the official Open Group list.
Within Oracle, Solaris is in maintenance mode. Almost exactly six years ago, we reported that the next major release, Solaris 12, had disappeared from Oracle's roadmap. HPE's HP-UX is also in maintenance mode because there's no new hardware to run it on. Itanium really is dead now and at the end that's all HP-UX could run on. It's over a decade since we reported that HP investigated but canceled an effort to port it to x86-64.
“What is dead may never die.” - House Greyjoy