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I think the way this currently works is fine. If someone wants to tip someting they can find your address in either your profile or your signature or plain ask. Its already as easy as copy & paste. The only "advantage" to an implemented system would be that the tipps are public. Tiping is usually not done in public though. Think about it. When you order a pizza (or sushi or whatever you like to order) there is the moment when the person says
that'll be XY and the most common way to respond is to hand one or more bill(s) and state
Y in return please (or something along those lines). You never publicly state the amount you tip. Same in bars and restorants. Why would you want to change this?