Has anyone ever tried making a two-piece backpack system where:
Piece 1 is a stiff frame and all the pads and straps that snuggly hug your body
Piece 2 is just a big storage compartment, which can be detached from Piece 1.
I realize that the number-one concern in a backpack is getting close to your body and supported in a way that doesn't stress, but it still seems like you could have a Piece 2 that you "slide in" to a series of straps on Piece 1 and then cinch them up so it's tight against your body.
If there are some commercial offerings like this, please post them to serve as inspiration.

