Reaper Steve
Explorer
However I don't think that will work out. PHB/MM/DMG are always the top-sellers in every edition.
True, but that's because those 3 books are the game.
My point is that it's past time for the info to be reorganized in its presentation. In 1E, the Player's Handbook didn't actually have the rules of the game... that was found in the DMG. But over time and editions, theywisely moved the rules to the PHB. In 4E you can play D&D with just the PHB and MM. But that means that the DMG was struggling to maintain relevance and necessity.
I think WotC finally saw that and figured out how to make the break. The rules of the game stand alone, regardless of classes, hence the RC. The newly released (at premium stores) DM's Kit is not necessary, but WotC has embraced the fact that it's not necessary, which resulted in a product and book that is much more GUIDE than any previous DMG. And I mean Guide in a good way... by focusing on guiding DMs without having to contain the core rules, the product can really improve a DMs skills.
Will we continue to see player books, DM books, and Monster books? Absolutely. But now that the core is self contained in the RC, I think the purpose of the DMG has changed, or rather, it can finally do what it was intended to do.