Some ideas you present are not bad. The idea of letting people generate SBD by sending Steem to the smart contract is good. The problem, why limit it to Steem? What backs Steem then? If Steem were backed by SMTs and not just generated out of thin air then this might work but when Steem is being generated out of thin air of course it doesn't work.

Interest has to be paid for the simple reason that if you are pegging to something unstable like the USD then you are already losing wealth for anyone who holds their life savings in that peg. If there is no interest then no one will be willing to choose this over Dai or over a lot of other better things like gold. I do know you need a plan to generate the interest and this can be generated and the revenue from that generation shared as interest.