The problem is that when a company goes big and someone gets a good exit they personally own that money until they make good on their secondary agreement. It would be easy to rationalize that it was specifically their personal hard work that helped make the company succeed. And since it's their money they have a big enough war chest to fight giving it to the pool. Or they can just skip the country. If the payoff is big enough there are plenty of folks who wouldn't mind trashing their reputation. And then that's the end of the pool.

Don't get me wrong, it seems like an interesting idea. I would love to have some way for my un-diversified work portfolio to get diversified. But short of creating a sweat equity only market/exchange I don't really know how you'd do it.

Even that has problems because people could fake a startup well enough to gain access to the returns creating a free-rider problem. It's probably easier to cook up a bunch of buzz and interest over an orchestrated 3 month campaign (esp. with a Kickstarter) than to actually do a startup. And since you're faking it you can promise the world and raise huge money from unsuspecting dupes with no intention of (much less a plausible method for) making good on your promises.