[djoldman]

Isn't it possible to actually code it into the ethereum contract to send eth to a wallet when it's traded?

[sneak]

In theory. I've not seen a contract that does that, however.

This doesn't mean they couldn't exist, just that (in my current understanding) it's not part of the ERC-721 spec.

[tsimionescu]

How would that matter if it's traded off chain?