I will try to help you out with this question.
There was a public roadmap released 2 years ago and remains of its existence can still be found on google (eg https://blogs.oracle.com/solaris/new-sparc-solaris-platform-roadmap )
However the page does not exist anymore: http://www.oracle.com/us/products/servers-storage/servers/sparc/oracle-sparc/sparc-roadmap-slide-2076743.pdf
The only official documentation which can be found:
List of Supported Oracle Hardware (With Last Ship Dates Announced) (Doc ID 1450710.1)
and the End of Life Server Products https://www.oracle.com/servers/eol.html
I hope this helps.