This is something I've been wanting for years, finally got to searching for existing feature requests :)
My usecase is not a problem with the rotation tags, but camera itself being rotated when I'm shooting images backwards, or in some other direction that requires twisting my arm.
User interface: for me, just rotate 90 deg left/right buttons would suffice. Something like icons in Gwenview, just without the text: https://masonbee.nz/wp-content/uploads/2020/06/gwenview_screenshot-1024x556.png .
For me, rotating a single image is useful.
I personally don't have a need to modify the original image, and I haven't seen a need for flip/mirror.
Attaching an example from one of my mapping sessions where rotating 90 degrees would make the image much easier to interpret.