marc@uberbox.orgOf course there already exists a way to thank IP editors. It is to go to their talk page and leave them a message that says "Thanks for your edit here [link to diff]." It is far more personal, far more likely to encourage the user to edit further (and maybe create an account?) based on research on the effects of template versus personalized talk page messages to new editors, and doesn't require anyone to write any code whatsoever.
I'm not entirely certain it's a good idea to "technologize" such very basic user interactions. It takes as much work to "thank" someone using notifications as it does to leave them a talk page message.
Risker/Anne