I don’t know the proper solution to those problems, but I use some workarounds:
- 16k sky textures: A sky dome composed by two hemispheres (with proper UVs). I divide the texture in Photoshop and apply each 8k half on each hemisphere.
- HDR as traditional texture: I convert them to EXR (in Photoshop). EXR textures won’t be imported as cubemaps and they’ll keep the high dynamic range.