“ethDAI is digital credit, leveraged from existing assets in one’s portfolio excluding ETH (remember, one wouldn’t lock up ETH to borrow ethDAI, just as they wouldn’t lock up USD to borrow DAI).”

Not sure that I entirely agree. With the launch of Multi-Collateral DAI various assets will be used as collateral in both usdDAI and for any potential ethDAI — IMO, for ETH to retain intrinsic value under a future system where the vast majority of tx’s are occurring off-chain (Layer 2), meaning limited tx fees for Layer 1 validators, and where ethDAI is being used as the primary means of exchange/currency in the ecosystem, then ETH must be retained as the *primary* collateral of ethDAI. If, however, as you say, ETH itself is being used as the primary means of exchange/currency in such a system, then yes, ETH should not be the primary collateral for ethDAI. A small caveat worth noting I think.