So here's how it works. If only one person is streaming, they automatically get played. If there is more than one stream online, normally the stream with the highest viewership gets the top spot, 2nd highest gets second, and so on.
However, I can basically "rank" streams to show up in the homepage player automatically whenever they are online via featuring them and ranking them that way. (This ranking is not the order on the left, and is not visible to anyone except me.) Right now, Jcaesar's stream for example is featured because he has been streaming alot of Project:M. So if I were to stream Starcraft 2 as I have been recently and were to have a higher viewership than Jcaesar, Jcaesar would still occupy the homepage player even though he had a smaller viewership. Using this ranking thing I can rank lower those who less often stream smash, and prioritize those who always stream smash. If there is a special event going on then it is easy to bump people up.