Why don't we consider other sources than rewards? Consider: rewards are incentives for effecting benefits for Steem, things that tend to increase it's value. Why diminish them?
Development has not drawn from inflation to date. Instead Stinc has directly funded development by spending it's stake. This discussion of using inflation/rewards to fund development is NEW. That is not how development has been funded so far, at least not by those developing Steem itself.
Using rewards to fund development is not necessary. Rewards are critically important to create value of Steem. Consider that other sources besides rewards have always been the source of funding for development, and may remain the best options today.