This is indeed useful. I would just add that there are many other ways to improve depth cues or make the images easier to interpret. For example, we recently added colored volume rendering and ambient shadows (see some example images here and here), which can be used in addition or instead of stereo volume rendering to greatly improve understanding of the 3D renderings.
I agree, these are two quite distinct use cases. The HoloLens is already proven to be useful for large and superficial targets, for low-accuracy applications (e.g., give confidence to surgeons in determining skin incison location), but may not be ideal for microsurgeries.
Lots of solutions were developed for displaying image overlay in laparoscopes or microscopes in the past 20 years, but they have not become widely used clinically - probably because they did not work that well in practice. Seeing recent progress in imaging AI, it is quite likely that real-time AI image annotations will become available in products of all the large laparoscopy vendors within a few years.
To add AR to surgical loupes, maybe the easiest solution could be to use digital loupes (like nuloupes or mantis) and external tracking.