The feature is only on SPARC, not x86. Oracle killed in-house SPARC development in 2017, and they abandoned OpenSPARC after they acquired Sun, so it's effectively a dead architecture. The software won't work without the hardware to run it on.
Finally, it is up to Intel and AMD to come up with hardware memory tagging, so far they have messed up all attempts, with MPX being the last short lived one.
Fujsitsu also does SPARC, and contrary to HP-UX, people still do buy Solaris.
EDIT:
https://www.oracle.com/servers/sparc/
https://www.fujitsu.com/global/products/computing/servers/un...
Finally, it is up to Intel and AMD to come up with hardware memory tagging, so far they have messed up all attempts, with MPX being the last short lived one.