The problem are the folks who damage, steal, and otherwise cause havoc. Usually loaning anything out is fraught with problems. One exception is "The Cable Company", which seems to have figured out how to loan out cables without suffering for it.
If some billionaire crazy wanted to do it. Best bet.. BUY "The Cable Company" plus some other audio store already doing well, (to acquire loan items wholesale, and just expand the range of items available for loan, gradually. The Cable Company already has the working mechanism in place... For billionaire, why work to start from scratch when you can just buy it ready going.
I also think one would need to work up to borrowing big money bits of kit. I had already spent a medium fortune before my dealer out of the blue offered to let me try something at home no strings except bring it back in five days.