I cannot say anything against Rok's idea.
Maybe the fact that already higher ranked players will have a hard job to get into PO. For instance, 4 people in front of me in the total stats play their 30 games, have 70% winning ratio (just an example) so I can only get into PO if I am in top 4, which is very hard considering that I get 5-10 points for my victories and lose like 60 when a newbie happens to beat me in Hysteria.