What does the poor eyesight have to do with not being able to wear sunglasses?
There are prescription sunglasses for shortsightness, astigmatism, etc.
So the sunglasses-form VR would just have to cater for that. Apple's headset-form VR already does (offers the option to have prescription lenses in it).
With extreme corrections it get harder to put that into anything other than flat lenses and a lot of sun glasses aren't that shape. I recently went through getting perscription safety glasses and had to get special inserts to flatten out the lens profile to make my relatively minor -3.75 to -4 prescription. I was able to get some relatively normal Oakleys in my script for sunglasses though.
Also you generally want sunglasses to be much wider and taller than prescription glasses, because otherwise you get too much light bleed around the sides. Making large lenses is when the thickness takes off, especially for nearsightedness where the thickness ends up at the edges of the lens.
There are prescription sunglasses for shortsightness, astigmatism, etc.
So the sunglasses-form VR would just have to cater for that. Apple's headset-form VR already does (offers the option to have prescription lenses in it).