is there a direkt exchange planned from PPP to a fiat?
I'm not quite sure, but if you want to invest in Paypie you need ETH. Ethereum can be obtained on shapeshift or coinbase for USD and then you will be able to invest

I imagine that there will be an exchange inside the ecosystem, only for the companies that use it, and even perhaps the ones that require the feature, I don't think is for the public, the public will have only the tokens on exchanges, then you can use fiat.