I think there is a some value in a tiltable viewfinder. Basically any time the back lcd won't do it and you don't want to get down to the camera's level. Using a camera at waist hight on a tripod in bright light is a good example. The evf can be really useful for reviewing images when you can't see the screen (too bright out or too much glare), or maybe don't want to mess with your composition, and the tiltable lcd screen would be distracting to others (i.e. shooting nightscapes with others). I think two of Fuji's medium format mirrorless cameras can use it: https://www.bhphotovideo.com/c/product/1311711-REG/fujifilm_16536922_evf_tl1_evf_tilt_adapter.htmlWell, I prefer looking through the 5Dmk3's viewfinder as well, question is why would you like to change the viewfinder's angle?
I understand looking forward through an E/OVF, I understand waist level viewfinder (= screen facing up), I don't understand having to face down and have the camera against one's face.
I would definitely use that feature often, but I can see how some wouldn't bother with it.