I don't really like to see the .sr-only is overridden, also .sr-only-focussable should be taken into account. On the other hand this construction makes it hard to theme the .sr-only element, even with utilities (specificity of 1,0,2,0 vs 1,0,1,0)

Also, I doubt this is really needed, quoting @patrickhlauke (#27986 (comment)):

I'd note that reduced motion is primarily about stuff that can cause trouble (read: feelings of nausea etc) to users with vestibular disorders, so mainly animated scrolling effect, accordion-type panels that animate open/close, etc.

The spinner animation is rather subtle.

I understand, and globally agree with your arguments.
This will probably land in our fork so I preferred to suggest this directly here :)

Let me know if it still sounds interesting and needs a rework, though.

Gonna close this for the reasons I mentioned above. Thanks though