For a while now, One Page Rules has made their own form of miniatures game rules based on other game systems out there. With the release of Age of Sigmar, this tradition continues. Page of Sigmar is now available to check out and download from the One Page Rules website. They've also made a statement about their rules based on Warhammer Fantasy Battles.
Long story short, their rules for One Page Fantasy Battles and One Page Fantasy Skirmish will continue on. They're not going to be taking away your ranked, regimented, fantasy battles that you've been enjoying. Also, unless people ask, One Page Rules will not be making rules in those systems for the new armies coming out for Age of Sigmar.
As for Page of Sigmar, itself, those rules have been condensed down to just 1 page and have modified victory conditions and terrain rules. The Warscrolls that Games Workshop has made are what should be used with Page of Sigmar. One Page Rules won't be coming up with points costs for everything, so they recommend using armies of roughly like-sized and equivalent forces in order to keep things balanced.