As SP weights VP, there is a mechanism for mining the rewards pool, as well as potentiating a hostile takeover of the blockchain. Only delinking SP from VP will eliminate this particular mechanism for profiteering, and protect the witnesses from just being purchased.
It is a radical overhaul, but, have no fear, it isn't going to happen, because those that currently control the witnesses are those most profiting from it, and from the golden parachute of a hostile takeover.
Rewards can still be delivered through VP from the pool if VP is equal, or weighted via reputation, and Steem can still be the best crypto on the market, without creating vectors for profiteering from vote selling, self voting, or other such mechanisms.
We see that such mechanisms really aren't 'self-sustaining' at all, but rather eventually erode the content creation mechanism by discouraging authors because the rewards mechanism isn't rewarding them for producing good content, but being mined by profiteers.
I do not see that any other means of preventing profiteering mechanisms and securing the witnesses from hostile takeover might succeed. There remain other profiteering mechanisms, such as botnets, that my proposal wouldn't affect, but these can be (and will be, eventually) dealt with in other ways.
There just isn't any other way to stop profiteering from mining the rewards pool and discouraging content creation that I can see.