The problem is that someone who has committed themselves financially to what is basically a set of hardware drivers with bells on, could quite rightly be entitled to think - "hey I contributed to the development of this software and now I can't upgrade to it!"
You can upgrade it, but you may not like the terms if you don't have a PPC
or are not interested in MOS, just like noone will be able to upgrade
OS3.9 while he is running on a 68k or x86-based emu.
Can you upgrade Win3.0 to WinXP using your 286 ?
Everyone who bought CGX_V4 did it to serve him on one job and that is
allowing him to run his GFX-card under OS3.x , and CGX_V4 does that,
and won't stop doing it just because V5 is released for a different OS.