It means basically that he can give up any other title, wait for Pacman to vacate the WBO or a 0.1% chance that Pacman kicks his head in for a huge purse. Worst outcome is a vacant shot that's easy to win against an unknown, then another paper champion. Some fighters earn the rankings the hard way, some seem to just end up at number 1. You have to take some of the WBO rankings (and others) with a pinch of salt, even if they have the best champions. People have to realise that having a belt or belts means nothing. The great but unpopular fighters will always be ranked low and won't get the chances others get.
new IBF & WBA rankings added. also have added opponents rankings. shows how important some fights are.