Very interesting. One idea, which is maybe a little bit off-road. Why are new STEEM produced when exchanging SBD for STEEM? Why not take these STEEM out of the rewards pool. Exchanging would then create STEEM demand instead of supply. In such a scenario inflation would be completely under control and price would rather go up than down when exchanging.

One could restrict the share of STEEM available for trading of this kind to some amount and thus leave enough for 'real' rewards.

But maybe I have't really understood the system and this is completely off.