They are calling it bonds because they are literally bonds https://en.wikipedia.org/wiki/United_States_Treasury_securit...
Default should be an unusual or unexpected outcome, not part of the contract. You don't take a loan from somebody and then saying them: "you know what, if I will not return you money in 5 years, even if my company still operating - write it off."
If the expiration is part of the contract, then it's a derivative contract. In this case you have only 2 outcomes: either you get paid 1 basiscoin, or your "bond" expires worthless after 5 years and you get nothing. That's why it's a binary future. Binary futures/options and prediction markets are illegal in US since they resemble gambling.
Sounds like credit default swaps ... you pay a premium until expiration (you get nothing) or some credit event happens (e.g. default; you get a payout). Difference seems to be the conditions for a payout.
Even if basis "bonds" were credit default swaps, and then listed on crypto "exchanges", they're still falling under the regulation of CFTC. Those exchanges need to be licensed as Swap Execution Facilities (SEFs). And if basis doing on the protocol level like MakerDAO - they need to get SEF license by themselves.