My concern is that I think that the referral program should not be open-ended. There could be a fixed period of time set for it to operate to generate viral growth (which could be extended if necessary).
Then should come a point at which BitShares will grow on its own merits as the best system available (ie., once there is a critical mass of users), and then ALL of the transaction fees should go to the blockchain (be burned) to grow the value of our investments. After all, the DAC is meant to be profitable for the shareholders, not just for marketers (referrers), especially after they are no longer needed.
For example, I don't think that anyone is still be paid to refer new users to paypal, are they?