If people are living off it and not powering up any, they aren't going to live off it for long.

That's a very important point.

Even if the user base and nothing in its behavior changed, it would become progressively harder to earn STEEM and SBD simply because the rate at which they are minted steadily goes down making competition for the rewards stiffer. Another important thing to keep in mind is that as the fiat prices of STEEM and SBD are speculative, the platform must grow in order for the speculation to continue and for the currencies to retain or increase their value. That, too, will make earning through producing content increasingly difficult. Also, rewards for earning largely depend on being noticed and appreciated by high-SP holders. When your earning potential is in the hands of the mere whim of a few people, your position is precarious.

Steem Power is king. (It is smart to divide it across a few accounts for security reasons but that's a topic for another time.) As time progresses, I predict that if this platform delivers on its promises, amateur content producers will be gradually squeezed out from gaining rewards by professionals. Those of us who have had the opportunity to power up and have chosen to use it will increasingly become investors and earners of passive income. I'm hoping that the Steem blockchain will power thousands of applications some of which have millions or tens or even hundreds of millions of users 5-10 years from now which will support a double digit STEEM price not through speculation but steady external revenue flows from real world value produced. I will be very satisfied if my investment in time and money results tens of thousands of euros earned annually as capital gains within that time frame.