Thanks for the in-depth answer.

• ETH-WETH is definitely traded in/out 1 for 1.
• Interesting about PETH. Considering that some people are facing potentially massive capital gains by opening a CDP with early-bought ETH, it'd be worth it for them to consult a professional to be sure.
• Even more interesting, CDPs sorta fit two out of those three. There is definitely interest, which can be paid at any time, and if the collateral falls in value, it will be seized. But there's no set maturity date. Which makes me wonder if it's not a loan, and instead just a fancy margined long position.

If you're curious, the Maker team goes into more detail in its whitepaper: https://makerdao.com/en/whitepaper The Maker team itself has not released any tax guidance of its own, for understandable reasons.