FYI the current SBD design is different from that described in the earlier version of Steem White Paper.
The WP suggested the(partially) compulsary conversion from SBD to Steem Power in case SBD debt ratio couldn't stay below 10%.
So, in the current situation instead of getting 65 cents for 1$, you would get 1$ for 1$, but locked in SP for 2 years ( initially it was 2 years, not 3 month we're having now )
However this part was actually never executed in code.
Updated: it wasn't the WP, the gradual forced redemption of SBD for SP was just a proposal from Dan Larimer
https://steemit.com/steem/@dantheman/steem-dollar-stability-enhancements