Updated Oracle Roadmap Points To Post-11.4 Solaris Release Around 2020
By now you should know about Solaris 11.4 that is currently in public beta.
But their March 2018 road-map update now indicates a "Solaris11.Next" for H2'2019 or H1'2020. Note that it's a "11.Next" and no mention of Solaris 12. It's still not clear if a Solaris 12 will happen given all the rumors following the mass layoffs at Oracle over the past number of months, but at least for now it's looking like it might be a Solaris 11.5 release around the end of next year or in early 2020.
That same roadmap indicates a "Eng. Systems M8 + Next Gen. Storage" in the solid 2020 time-frame or even early 2021.
Positioned similarly for 2020 or at the edge of 2021 is "Servers M" also on the hardware front.
The March 2018 SPARC/Solaris road-map in its current form for March 2018 can be found here (PDF), but it's certainly subject to change as we've seen with the tilting SPARC and Solaris landscape especially over the past year.