So I guess for starters you will need a coin you can mint more of as needed, so that any time its value tries to rise higher than the fiat you are hoping to "peg" it to you can mint more to sell to try to bring the price down to fiat-parity.
Lets suppose that I sell $1 USDe to Party X for $1 USD (I now have one dollar and he has an electronic copy), Party X in turn trades his USDe with Party Y for legal goods and services. Over time there might develop a secondary market for the electronic copy, lets say in Japan, where Party Y could sell his USDe to Party Z for $1.05, even though Party Z knows that Party X only paid $1 for the USDe. That would be of no interest to me... because I only would have a legal obligation to give Party Z $1 USD if he should make demand for exchange. In other words, I would only have to "peg" the exchange (1 USDe = 1 USD) ... who cares what happens in the secondary market? The real idea would be to facilitate trade efficiently and effectively.