Ranked battle sps has always been planned and is in the white paper. There is a set amount allocated to this. As stated in the article and in the white paper, the pool is 7.5mil a month and i would imagine will go on until this particular distribution method ends as stated in the whitepaper. Sps still only has a max supply and this was always the plan to be implemented once the airdrop ends. It will also be part of guild brawls at somepoint.