Well, your concerns make sense, to say the least.

Not only is it difficult to reach an equilibrium (because reaching an equilibrium between professional knowledge and spontaneous online social interaction is, I believe, an optimum goal for a sustainable Medium), but it is also nearly impossible to know whether you have reached it, how you can reach it, and how you can maintain it.

It's like in economics, where equilibrium is where supply meets demand. It's an optimum point that is determined by market forces. Suppliers and buyers negotiate to reach that point, either implicitly or explicitly, but they can never be sure, unless through experimentation, i.e. price adjustments, etc.

A successful Medium in the long run should be able to identify the equilibrium point between the supply side, as it is represented by writers, and the demand side, as it is represented by readers.