Any peg requires a trusted third party. It would be like tying gold certificate ownership to cryptocurrency tokens, like colored coins. And when you have that

Any peg requires a trusted third party. It would be like tying gold certificate ownership to cryptocurrency tokens, like colored coins. And when you have that trusted third party, why do you have independent miners? In other words, you get Ripple again rather than Bitcoin or an altcoin. You drop the decentralization.