I think QNX would be a poor target for removal up front. It's a mostly POSIX-compatible system that runs on modern embedded hardware very well. ( http://www.qnx.com/products/neutrino-rtos/neutrino-rtos.html#POSIX ) If your desire is to make Perl more relevant, abandoning a system with decent although small market share on ARM Core and Intel Atom systems is probably not a good way to do that. Should the GNU-userland Linux systems, the BSD systems, OSX, Windows, and maybe Android be higher priority? Sure. But to get to all of those portably gets you a pretty long way toward QNX. If support for it fell off it may not be a catastrophe. Writing it off before any attempt to gauge the work necessary to keep it seems premature.
VMS may not be cutting edge, but it's still used in some important places.
I don't imagine it would be hard with a Windows version and a GNU userland installed on top of their OS to keep the eComStation die-hards interested in maintaining the OS/2 and eComStation portability. It's not a very big community, but it's still fairly active.
I think if you wanted a better list of systems to abandon for being irrelevant you could start with MS-DOS/PC-DOS, AmigaOS, Haiku, Mac OS Classic, and BS2000. I almost included RISC OS. Their community seems pretty headstrong and there's still work going into the OS.