But just because he is worth a couple billion does not mean he has $500 million to throw at a windmill idea. At heart, Cuban is a businessman (whether he is a good one or not, I will leave to others to argue about). He failed in his efforts to buy the Cubs. He failed in his efforts to buy the Rangers. He has failed, thus far, in his stated goal of making the Mavericks champs of the NBA. Cuban talks a lot, be even he is not stupid enough to throw large amounts of his money into non-economically viable business ventures.
No one has a greater economic interest in a playoff than ESPN and ESPN has far greater access to "capital" (Cuban's word, not mine) than Mark Cuban does. If there was a simple business model with a 12 or 16 team playoff that is both fairer to all 120 FBS schools than the BCS and more beneficial to the major football schools, ESPN would have been able to convince those schools to move to a playoff by now. Over time, additional "tweaks" to the current system will be made that will move us closer to a playoff, but those changes will largely need to preserve the entrenched interests of the major football schools.
As for blackmailing the major football schools into accepting something they do not want, I wish Cuban good luck. The top 10 programs alone bring in over a billion dollars per year. It would be a fool's errand to pour $500 million into a project that effectively is a plan to bribe and/or bully the major football schools into doing something that is not in their own best interests when those schools generate more than twice that amount of money every year under the current system.