If they're going to cash out immediately, then they should probably offer a 50/50 payout of SP and STEEM. The STEEM can then be transferred directly to an exchange and sold. If a user wants SBDs, they can buy them on the internal exchange with their acquired STEEM. This would require actively seeking and purchasing SBDs, which should reduce the overall supply being created and held, I would imagine.
Adding an extra step almost always makes it less likely that the extra step will be taken. This is probably why we don't see many new investors of STEEM in the first place. The added step of buying BTC in order to buy STEEM essentially serves as an extra barrier to entry. I don't see how it would be any different for SBDs.
SBD supply and debt ratios can be managed. It just takes a little more effort to make that happen.
I edited my original reply, I had a typo in the second option.
Its the extra step of having to convert Steem to Steem dollars which I think is the problem. Its easier to understand if you just get paid in steem dollars. Basically for most people its the same as getting paid in dollars (i.e. its worth the same)
I think people would be happy to pay a small % fee for not contributing to the platform in terms of steem power. It would be easier to understand for them. I am referring to people not into Cryptocurrency.