What are you talking about? The DMG has fairly extensive rules on making your own monsters. Pages 184-185. All I want is a traps and hazards equivalent of that, and I'll be extremely happy.Here I'm much less sure. In fact, I wouldn't hold your breath if I were you.
Rules for creating monsters, weapons and stuff from scratch simply seems to not be on WotC's agenda.
Apart from "look at a similar monster/trap/etc and start from there" of course.