It's almost a guarantee that X and Y will have their own guidebook. I doubt I'll be buying one though. Unless you're a collector, buying the guidebooks are just a waste of money when you can find everything online, and for free no less!
Like most guidebooks before, I expect these to have details on all of the new Pokémon, a complete walkthrough of the game, and detail on the region map and all its different locations, as well as other secrets that you won't typically find so easily. Not to mention, explanation on new game mechanics and features that will be introduced. There will definitely be some good stuff in there, but again, nothing you couldn't generally find on the internet nowadays.
Oh, and no guidebook is ever complete without a complimentary poster! Got to have one of those in there.