The more I think of this, the more I think it'd be a good idea in a couple years and the more I think it won't happen.
There are a number of changes that could be made to the game. Small, tiny revisions and larger clarifications. Fixing the monk, revising stealth, incorporating the errata, etc.
There is some content and options in the Advanced Player's Guide and Ultimate Combat that pretty much should be core. Things like traits, archetypes, the extra CMB options, and alternate racial traits could be worked into the core rules, becoming a tighter part of the game.
At the same time, it might be good to split the Core book into a much smaller Player book and a GM book. Even with the Beginner's Box, the Core Rulebook is daunting and huge.
This won't happen in 2013. We know all the books for that year. We have Ultimate Campaigns and Mythic Adventures.
2014 would be the year then.
However, that's the year of 5e and we still don't know what Paizo's plan with 5th Edition is, or how WotC is going to handle that edition's OGL/GSL.
If 5e is everything it can be (or even half) it might really steal Pathfinder's thunder, really pulling players away from Paizo. This might not be a bad thing, freeing Paizo to just focus on what they want to do, what they do best: adventure paths and the Golarion world.
Even if Paizo doesn't decide to refocus Pathfinder and keep supporting that game, releasing a competing product in the same years as the new D&D game is ballsy at best and foolish at worst. You just can't compete with the D&D core rulebooks.