[luminiferous]

Question: since bills can be either loaded or unloaded (either because they haven't been put in circulation yet, or because they're counterfeit), doesn't that mean that e.g. a vendor taking my Kong who has no trust in me would have to individually check each bill via NFC or i2c to make sure that the contract backing the bill is valid (and the correct amount, etc.)? And that I would have to do the same for all the bills I get back as change? As a completely trustless transaction, this seems like it could be entirely too slow for most applications, without some kind of device to quickly verify multiple bills.

[ccamrobertson]

Ideally you should check every Kong note. In reality behavior would probably be similar how bills are verified now; businesses regularly check $100 and $50 notes under backlights and with special pens but don't worry about lower denominations.

A dedicated "Kong scanner" could do this very quickly.