Charly Ghislain:
I have nothing against this proposal although im not sure it would be that much efficient. Especially, how does it make relay operations 'less sustainable' or 'more risky'?
I assume you mean "make _malicious_ relay operations 'less sustainable' ..".
It would be less sustainable because they would have to run relays for longer before they can start exploiting tor users. And "more risky" because physical letter delivery requires them to pay someone and hiding money trails is usually harder than hiding the origin of someone creating a random email address.