This is one way to do it, however that requires us to hard fork and allow them to create coins out of thin air in our blockchain (I don't have a problem with that part theoretically, being that the coins would be tied directly to a proof-of-burn in the Bitcoin blockchain). However, here's a problem with doing that, for example, what if a whale brought over 75M worth of Bitcoin and instantly controlled 75% of our network's masternodes (with our market cap at 25M)? That sounds like a sybil attack vector.
If they tried to buy the 75M from a decentralized/centralized exchange, they would simply run out of money.
Yah, I'm glad you can think so deep, it's probably way better to have an exchange that runs off of smart contracts or some such. Where coins are locked while up for sale, and released to new owner when the sale is completed via matching terms with buyers and sellers. The bids are matched and ownership of coins is switched. This would be much cleaner and I can see it being totally doable. Plus, once something like this is implemented - probably directly from the wallet, I can see the same structure used for a lot of other types of trade/contracts. But certainly, this kind of exchange could be done completely decentralized and in the wallet or wallets.
This kind of solution could be just like existing centralized solutions, with real time data that anyone could tap into to provide charts, etc... I'm surprise it hasn't been done before? Are contracts like this still buggy?