I would argue that the handling of fiat should be completely decoupled from any future exchange, P2P or otherwise.

We let dealers/brokers/banks/mtgox handle fiat. They can worry about regulations, AML compliance etc.

When we deposit $ with them, they give us a colored Bitcoin or an alt-chain coin that is backed by our deposit.

Once we have our MtGoxUSD coins, we can trade in real-time on the P2P crypto currency exchange. No waiting for bank transfers etc.

So perhaps efforts should be focused on creating an open source crypto-coin-only exchange. It does not even need to be P2P for it to be useful.