You raised very important points and questions. As I was working on a potential new feature for communities, I have also been thinking about a potential separation of utility. STEEM remaining resource token and other SMTs could be various utility tokens.
There could be SMTs based on:
attention value; that has native ads (an optional feature I'm working on for hivemind communities, details on my blog). Could be zero inflation as well.
subscription model; where a unit of SMT represents a membership and certain rights within that community
and more...