ktx2 support in cmgen.exe?

[emezeske]

Is your feature request related to a problem? Please describe.
(I formerly filed this as a discussion in #8432, but am moving to a github issue)

The problem I'm having is that the ktx1 output files from cmgen.exe are very large. Even at small resolutions they often eclipse the file size of the full-resolution equirect image that they are based on. It seems that maybe the ktx1 format does not offer compression?

Describe the solution you'd like
If cmgen.exe could output to ktx2 format, it seems that the skyboxes/ibls could be compressed with basisu and thus be much smaller.

But I'm not at all an expert here, so maybe there's some reason it can't use ktx2? In that case is there another format that would compress better?

Describe alternatives you've considered
I haven't thought of any other solutions. Possibly there are other container formats, etc.

OS and backend
Not OS/backend specific.