> when do OS4 users get to use all that GFX RAM themselves?
They can (and if they pay A-Eon, also do) use this since 2016 with Warp3D Nova, which allows textures to be stored beyond the former 256 MiB limit.
> It is just plain overkill IMHO
Beside the larger VRAM, newer graphics cards have the advantages of more recent OpenGL standard (for ports of modernish open source games) and hardware video decoding to relieve our decrepit CPUs (the newer the GPU, the more recent the supported codecs). All of this requires driver/software support, of course, but OS4 (rather 3rd parties) has proven that it's possible.
> Radeon AGP/PCI-X […] GFX cards
AFAIK, there's no such thing as PCI-X graphics cards. [Corrective edit: there is, but not MorphOS-compatible, see next comment.]
> a PC based compatible GFX card of choice, that is probably > significantly cheaper than a user would install in their OS4 > hardware, even if it is also MorphOS compatible.
Unfortunately, and as alluded to in comment #2, there's no overlap between GPUs 3D-supported by MorphOS and GPUs 3D-supported by OS4 (except ancient Radeon R200 series).
