I wonder how well NetBSD would run on it. There're quite a lot of current packages for it:
https://cdn.netbsd.org/pub/pkgsrc/packages/NetBSD/sparc64/10...
https://cdn.netbsd.org/pub/pkgsrc/packages/NetBSD/sparc64/10...
A lot of the "wow, this actually Just Works on OpenBSD!" support is because one or more OpenBSD developer actually runs the given system. Supposedly that's why there's really good support for a large number of laptop peculiarities that NetBSD lacks -- OpenBSD devs are actually dailying OpenBSD on those machines.