> (x) Ideas similar to yours are easy to come up with, yet none have ever been shown practical

Seems to me a very good reason to go ahead! It' less about the what and more about the how.

> (x) No one will be able to find the guy or collect the money

I don't see any problem there - all it takes is an automated response with a PayPal link

> (x) Many email users cannot afford to lose business or alienate potential employers

They are out of target anyway; this idea applies super-busy/famous people who can afford to lose a few messages.