You can't assume an efficient or even real market. Valuations are designed to benefit certain people. There's virtually nobody that would benefit from marking down the valuation of a company, and there are motivations that would lead to acquiring at inflated prices. For one, if you're buying something for the prestige of owning it you don't want to prove it worthless.
So, a startup that hires a bunch of developers to hack as a team on some open source project and fires quickly then flips the team to a bigger company[1] could work?!?
sadly, I thought of a domain name for this: teamchurn.com
It's only worth it because someone was willing to pay it. The last chump to hold the stock before the company unravels eats the loss. Early founders and VCs have cashed out long before that. It's an unfortunate game, selling dreams instead of substance.