So, you would have a direct financial incentive to do so, and no one would be able to stop you. This is the same thing that goes on with arbitrary banking fees worldwide, and the end user is powerless to stop the bank because they need to transact money. If you're sneaky enough about this you can do it under the guise of something like, "the PeerCoin network improvement fee that goes towards research, innovation, and development of the PeerCoin cryptocurrency."
Exactly. But even if you don't indulge in such schemes, including a transaction in your block at high volumes will cost you (high) personal expenses, while the beneficiary will be general public. Some people will inevitably cheat in these conditions, trying to parasite on the rest of the network. It will inevitably lead us to the Tragedy of the Commons problem.
A cryptocurrency architecture that relies on altruism while cheating can be beneficial to some extent, is far inferior to an architecture, where no egoistic behavior can ever gain you any benefit. I would not bet any significant fortune on the PPC because of this reason unless this aspect is fixed, and so would many other investors probably. Therefore I see not future for the PPC so far...