So you're complaining that something that we know (because we've been told by the designers) is going into the DMG isn't in the MM, and you're scared that they'll have to cut... something?
And you'd have rather they sliced a bunch of monsters out (which, I think you'll find, pretty much everyone else would hate to see) and made us wait for a year or more for them, instead of you just waiting until early December for what you have already been told they are delivering?
I understand your concern about the limited space in the DMG, but I think it will be fine. The designers and layout guys know where they have space and what they need to be doing with it. A list of monsters by CR (and terrain) will also be in the DMG- again, that's where encounter-building resources traditionally go.
Not to disparage your concerns, but to me, this seems like a lot of blustery wind without much behind it. You'll get your monster design guidelines soon enough. If you can't wait, check out Surfarcher's blog posts about it; they will help.