Could you be more specific about which SPARC chips you would like to see supported?
Bear in mind that it doesn't make sense for Studio to support chips on which supported versions of Solaris will not run. For example Studio 12.3 supports releases no earlier than Solaris 10. Solaris 10 has its own minimum chip requirements. You cannot in general run a program on an earlier version of Solaris than the one on which you built the program. So if a target system can't run Solaris 10, you can't expect to run a program on it that was built with Studio 12.3. Thus, even if we wanted Studio 12.3 generate code for old chips, we could not test the result, and you could not expect to use the result.
You can, of course, continue to run older versions of Studio with older versions of Solaris that support old chips. The software doesn't expire or stop working.
I am interested in UltraSparc IIIi - the latest Workstation chip. I know that it is really outdated, but this is a workstation, not server. So, people who run these CPUs can verify your wonderful compiler on workstation class software, such as Qt (I just filed a bug here), Firefox and etc.
I don't insist, but the more people use your compiler the better it will be. Also, besides Solaris 11 there are OpenSolaris forks on which can run your compiler even on old hardware.
So, I think, it would be better to leave support for old CPUs, if possible.