Demetrios1453
Hero
Updated. Mearls definitely said 3 on-stream, but apparently that figure was incorrect.
Personally, I'm a little surprised that this book includes both player options and DMing tools like traps and downtime tables. Volo's Guide was strange enough, combining player races with monster stat blocks as it did, but this seems even stranger to me. I've never really cared if players were familiar with monster stat blocks, because they'll figure those things out after playing long enough anyways. But traps and downtime are definitely behind-the-screen stuff that I'd want to keep out of the hands of players.
I imagine Mearls meant to say "up to three" and just had a misstep while speaking (we've all done something similar). And I'm fine with 25+ subclasses, which is, if you think about it, quite a lot, and should cover most if not all of the most egregious holes left after the PHB.
As for the book format, apparently that's the way it's going to be done from here forward, with both player and DM stuff in each book, presumably to make have something for everyone and thus increase sales. I'm not too worried about it - when my players page through my VGtM, they mainly focus on the player races and give a cursory page through of the bestiary section, but they don't sit down and read the DM stuff either in the first section or in the bestiary itself. I doubt most players will be doing any in-depth reading of the trap stuff and so on, unless they are interested in such things, which means they are likely potential DMs anyway...