I proposed something that was basically the same thing, but instead of cvTokens I proposed digital fiat which is issued when BTC is deposited into a pool.
https://bitcointalksearch.org/topic/a-proposed-method-to-facilitate-p2p-trading-between-fiat-and-cryptocurrencies-214431
Very cool, this is basically what I was proposing. You 'deposit' BTC into a pool by 'mortgaging' it and it issues crypto-fiat. Your idea used Open Trx and didn't allow for posting of additional collateral and thus downward deviations in the BTC price were directly reflected in the redeamability of the dUSD. It also required people to use 2 systems: Open Trx + Bitcoin and Open Trx requires federated servers which don't require "trust-per-se" but they are still 'centralized' and potentially a legal liability. I suppose an Open Trx server running behind BitMessage would be a start.
So to implement my idea in your terms you would deposit your BTC in an OT server. Then you would ask the OT server to mortgage your BTC for dUSD at 50% face value and you would end up paying interest for this privilege. You must pay interest because you are effectively 'borrowing' USD from the network (society) AND there is risk of default and potential for your collateral to drop by 50%.
Other people are willing to hold dUSD because it is paying them interest which makes up for the fact that there is still transaction friction between getting into and out of dUSD and the fact that they are exposed to some BTC risk.
Later when you want to pay off your mortgage you only get the collateral back that wasn't used to pay interest. You would pay off your mortgage because the collateral is worth more than the dUSD and thus you are motivated to accept deposits from people.
I just implemented all of this directly into the blockchain.