I'm sure I could, but I don't really see the point? NetBSD supports all of the SS20's hardware, except for the audio which I wasn't planning on using, anyways. Also, the only Sys V I've used is IRIX, and whilst the graphical parts of it are certainly decent, I have to say I find BSD much more pleasant, though I'm sure it's just familiarity. I need a UNIX box that's a serial console away from my Quadra, and this is a very good bet.
I'm nor really sure what Solaris, especially the newer version which are supposedly quite big, could offer me except for the concept of an "original" OS? I certainly don't have any Sun-specific applications that I'm wanting to run.