Funding the SPS from vested stake inflation makes way more sense to me than taking it from author/curation pool. What does a couple of % of inflation matter to a large investor when the variations in price on a weekly basis are more than that? I don't think it would even move the needle as far as an investor deciding whether or not to invest and stake a large amount of steem, while taking it from author/curator will definitely move the needle for actual users of the network.