It could be used just as a luxury thing....like taking helicopter rides for fun and stuff. You wouldn't get super high where the pressure is dangerous but just fly a little bit above a cool area, like a forest or something...
Well, they have glass floors at some towers, so people could walk on it for sure, and I'm pretty sure there are deep water subs that have glass windows. The bottom of the sea has a much higher pressure than flying through the air.
I think the pressure isn't the problem it's the vibration when you takeoff and land plus if there is terbulance the glass would be the structure of the planes bottom it would have to be able to withstand extreme vibrations (dirty minds i got it)
Well they could use a camera mounted on the belly of the plane hooked to a special monitor like some glass bottom boats do. It would be safe plus wouldn't affect the cargo space.
there would be nothing but the view of the luggage