But it isn't a startup, it is a currency, so it's much worse. J.R. could dump his stash to crash the price of MSC, which would result in cascading crash of all escrow-backed currencies.
Of course, J.R. isn't that dumb, but what if his private key is stolen? There is $20+M price tag on it now, it is sufficient to warrant highly targeted cyber attack or even physical attack.
It's a shitty situation.
The key feature of Mastercoin is in uses which depend on Mastercoin price, such as CFDs and escrow-backed currencies. Owner of a large stash of mastercoins can significantly affect the price, so it is absolutely crucial to secure these stashes.
(I don't think that distributed exchange is the key feature: colored coins are better at that, as colored coins-based exchange is faster and works with thin clients. But colored coins can't do what I mentioned above, at least, not now )