I may be talking out my a$$ because I haven't done any research, but from what little I do know about HP9000 and HP3000, the hardware is as different from each other as IBM RS-6000 is from S/370.

I think the only reasons why Linux made it onto the 370 is because there once was an AIX for 370 (could still be) and because of the existence of VM. AIX/370 simply said that it could be done. VM exposes architecture internals and provides a safe "playground" for sysprogs to easily steal a few cycles for experimentation without hurting production operations. Oh yeah, I forgot that IBM suddenly wanted it to happen.

So far as I know (and I admit that I don't know much), the HP3000 architecture is dying ([link|http://www.hp.com/products1/mpeixservers/future/details/index.html|HP Endgame Letter]) because HP wants it to die. Also, I don't know of any parallels to AIX or VM for the HP3000 line.

POSIX notwithstanding, I don't believe that HP ever had any commitment to put the words "open" and "HP3000" in the same sentence. I don't think IBM did either (with its 370 architecture), but in my opinion, their installed base made them do it.

I know that this is all anecdotal, "gut feeling" analysis on my part, but I would be surprised to see Linux ever make it to the HP3000.