I think the next client version/fork is to the right direction since the block signers will be a dynamic number... so we can have more participants...more difficult to control them.... am I missing something?
Cost. You're missing the cost it will take to maintain them.
Going back to the analogy that BitShares is a Company we should be looking to minimize costs and maximize profits for our shareholders. Factors in that formula need to take the marketcap into consideration, it seems to me.
Another perspective is to look at BitShares as a micro economy, which it is. In that way why would we want to control it or regulate it? Shouldn't it be self-regulating, i.e. a free market?
Yet resources like block production and delegate pay must be managed. It is fuel that makes the engine run. But the engine needs many things to keep it running smoothly, and how everything is balanced so it runs efficiently is quite a challenge, a very dynamic challenge, like when our engine is going up hill more fuel and air are required.
How many witnesses / workers / delegates are required? That's a good question, and one that will likely need to have a dynamic answer. What will the algorithm be for setting the right number at any point in time for the factors that affect system efficiency while maintaining system integrity?
These are weighty topics to be figured out, and it's gonna take all of us to do it, including many above my pay grade.