Earlier quoted context omitted.
Probably because collateralizing with the thing your borrowing is kind of pointless, yeah?
Oh yeah. I guess I assumed the thing being borrowed was off-chain (dollars, e.g.). My mistake.
So we think a really interesting use case in the short term is margin lending of crypto assets. Say you have 10 ETH and want to short-sell a different ERC20 token. You could lock up your ETH as collateral in a loan denominated in the other token, and then sell those tokens. If those tokens depreciate in value vs. ETH, when you buy back the tokens you'll have made a profit.