That raises a great point. Permanent payouts are a huge potential pitfall in that respect. They could become a very real issue that would present their own problems when abused. I think sometimes it's completely forgotten that the money has to come from somewhere because many users are are only posting, voting and flagging in the hopes of getting paid.
There's no actual exchanging of currency between two parties (voters and posters) so no one really cares what happens as long as the platform pays them out. The money is being paid out directly by the platform itself for user participation and even the short term model has already seen it's fare share of abuse. Extending the payout period would absolutely serve to further widen the potential window for such abuse.
After all Steemit isn't bringing in any money from ad revenues (like Facebook), or donations (like Reddit) right now, so all money that goes out has to be replenished in some fashion or the platform would die a slow and very expensive death. With a market cap of $180 million USD give or take, that's a whole lot of incentive to game the system to death by abuse, bots, or any means necessary to grab as much money as possible before the whole system collapsed.