This is an old thread but I quite like the topic so...
For the perfect hide, I think it would need:
-To be large enough for people to be able to sit or stand with enough space in between seats and windows to be able to keep equipment near oneself.
-To have windows at the correct heights, depending on the use of the hide.
-Possible species to be seen at the given hide to be displayed on posters on the walls and a whiteboard to write odd/rare sightings.
-Maybe separate sections for birders/photographers to non-birders? It's never fun when someone brings their loud toddler into a quiet hide, but then again seeing birders in action could encourage more people (especially youths) to take up the hobby.
-Coffee for sure, like stated previously in the thread by several people.
-That's about it. Honestly the purpose of bird-hides isn't for them to act as a lounge with a big window, but to be used properly as wildlife observatories. Nonetheless, a wet, uncomfortable and cold hide wouldn't appeal to anyone, no matter the location.