That brings up another important question. How do you find the ideal person to take a leadership role for development? That is where the credit should go, but it's a tough spot to fill.
You're confusing "my plan will work if other people behave this way" with "other people will behave this way".
Moreover, it's an open source project, so you can't say anything about "any ensuing corporation". You can only make committments for corporations that you control; you can't stop other corporations from getting most of the benefits.
And, who's to say that 6 is the right number? What if a given project takes 10 people to do reasonably? Why will those last four people contribute?
I guess 100% is the best way to structure it. Possibly even with a disclaimer saying the founder would not create any company out of the source code - but could be hired by anyone who does. The founder's role would then, simply, be an evangelist for the project(s).
I think the last four people would participate in the hopes of entering the top six, but a more open plan would probably encourage more participation. I think the last four would participate with the goal of entering the top 6, just like the dozens of applicants for the winner-take-all Ansari X-Prize.
I just think that having any plan for the future would make developers more likely to invest their scarce time.