I think I had found an Intel graphics card once that could run D3D9 (with software vertex processing and POW2 textures) and couldn't run GM.
I'm surprised GM works on them at all because of this limit!
It's probably not going to happen anyway. I mean - you can make something basic work for everyone (like making a D3D device) but it's simply impossible to get every feature (in every way) on every computer that supports 3D rendering. I think it's quite reasonable to disable mipmapping completely / force POW2 on older PCs.
to make sure whatever we decide works for everyone
Agreed. Though additional options to enable mipmapping in sprite/texture creation functions and enabling/disabling mipmaps at runtime (for those textures which have mipmaps generated) are as necessary as that, IMHO.
although I think I still favour something inside GameMaker that you "tick" for a sprite
P.S. One thing came into my mind just now (a bit unrelated though): I think it would help us find the location of many bugs if you could post information about what those errors mean exactly. Or, at least, more detailed error messages. They're quite cryptic even for experienced programmers. I'm seeing "unexpected error" and "runtime error 216" popping up occasionally along with GM hanging after FPU exceptions (or perhaps any exceptions) so I'm wondering about the exact nature of errors there. I think that could really help the creators of DLLs.