It probably works well until Bitcoin gets a piece of good press and another big cat comes along and says, "ooh, I want in on this. But I don't want to cause large price fluctuations with my huge purchases.... so I'll just buy enough to take down any large walls that pop up." Suddenly, with the walls gone, the price starts drastically going up and if the individual(s) that sold the coins wants them back, he'll have to buy them back at a higher price.