The modern SPARC platform ( sun4v ) is locked in Solaris. No chances for open-source OS'es like Linux or *BSD.
This is because the important hardware documentation is closed ( known only to Sun / Oracle engineers ). For example:
* virtualization features of CPU are documented only at hypervisor-call level (part of Sun servers' firmware), and only partially.
* CPU errata are closed ( Some errata for old UltraSPARC III were opened during OpenSolaris project, but that's all).
* crypto features ( SPU and MAU ) are closed.