I know that it is expensive, and I usually use just 1k textures, which are much faster to compress. The model I have used is from Kitbash and "pipelined" via (KitBash3D) Cargo and blender 4.1 (gltf-export) (I downloaded the 4k by "accident"). The problem with these models are that they use up to 200 textures which is very much and this is why I experienced the long loading time (with normal models with baked textures or lower texture count you might not notice it)
I know that bc7 (and bc6) are expensive, and you have done a great job with it. But I would still suggest some important UX improvements on this part:
The process should not block the editor
rule of thumb → if something takes longer than 100ms, show a progress screen with proper update/progress info
if it is non-blocking, show progress in the status bar with information of what file is processed right now.
In general, for a better UX you should report more info to the user on certain actions.
Just a few samples where this might apply:
Model/Texture-Conversion
GI-Building
Scene-Loading