Remember Populous only raised $10.5 million in the pre-ICO. This is pittance compared to what is required to funds the invoices expected. In my opinion, the funds raised are used to setup the team, offices, equipment etc. and most importantly to be able to buy trade insurance. Without trade insurance the project cannot get off the ground.

Therefore the money for funding invoices will come from elsewhere and only Populous will know where and fiat investors will be required. If the price of PPT on the exchange is $100, it does not benefit Populous because the money changing have is between the seller and the buyer with the exchange taking a small commission, Populous does not receive anything from this transaction because this money does not go into the liquidity pool. So making PPT a requirement to invest in Populous will not work because there is no liquidity as a result of the price going up.

Populous will still survive even if PPT goes to $0 because the liquidity pool is what is important. As the liquidity pool increases then PPT will also go up relative to it.