Blazer approved build, I like it too!
Piano hinges have their place. For the door on my dog box on the back of the Northstar I used a SS piano hinge.
Because it is the right hinge for that application.
For a sleeping platform it would work well also. But that application is different and not written in stone. I don't see why a removable pin hinge (actually several of them) wouldn't work. Gate hinges are generally heavy but generally have a high working load. I don't know why either one wouldn't work if you wanted to remove the extra platform. And that idea really makes sense to me.
There are a number of people that have built platforms with other types of hinges besides piano. I think most people get stuck in a box on design without doing needs analysis being done, at all.
Hopefully the last bit of snow in the yard will be gone tomorrow and before long I can get started on mine. Bet at least once a day I keep changing the design. Good luck going down the hinge rabbit hole
But you will have what works for you when you are done, not something that someone else designed for everyone else.
