Hmm yeah i guess you have a point. But it will be fiat with bitcoin properties (low transaction fees/times, anonymity, etc).
But how else you could fix it's price ? If you don't premine them, you can't possibly agree to buy and sell at a fixed price it would require billions on your behalf.
And about the pegged to fiat thing, if, hypothetically , the coin would get widely used, more then fiat, you could at that time untie it from that fiat, it wouldn't change its value if it would be that big.
Anyways , there's no solution to make a coin tied to a fiat, that is also decentralized ? Wouldn't such a coin be just awesome to exist ?
I think you need a strong background infrastructure at first, such as payment gateways for let's say BTC and USD, a regulatory apparatus (RA for short. This apparatus can be a part of the distributed client), a target value for BTC/yourcoin and USD/yourcoin rates, some premine plus some BTC and fiat as reserve. Then the RA can keep an eye on the payment gateways (exchanges) and it can intervene if the exchange rates shifted too much for a predefined time period. If the prices are rising too high then the mining rewards can be increased and/or the RA can automatically sell some coins from the reserve. If the price drops then the opposite will happen.
Maybe you should take a look at eMunie as it trying to achieve the same goals. (Currently in beta.)