I don't see Katy ever surpassing Rih in #1's.
All we know is that Dark Horse is going #1 and both their next lead singles probably will, then Katy has 9 and Rih has 14. Given the fact Rih is younger and will end up with a lot more era's than Katy, she'll probably have more #1's.
It doesn't really matter anyway, Rihanna will always remain superior to Katy in every aspect.