You say that the long-term weakening of SBD is a risk. Please consider the fact that long-term strengthening of SBD is also a risk, and I believe a damning one.

Your business model seems to depend on the SBD interest rate to fund your depositors' interest payments. Here's the problem: when you increase worldwide access to SBD by arbitraging between SBD interest rates and consumer banking interest rates, you'll (if you're successful) put a huge demand on SBD. This will cause the price of SBD to rise above 1 USD, and if it stays high for too long, the witnesses will vote to reduce the interest rate in order to encourage people to sell their SBD.

Put this another way: If SBD is low-risk, safe, liquid, and all the other things we associate with cash, then arbitrage opportunities will tend to drive its interest rate closer to the rates that banks pay. Please carefully consider the possibility that your business model may be self-defeating.