I wouldn't want this sort of book to include any particular sorts of traps, terrain, and hazards - It is the treatment of those things which I would rather the book focus on.
Rather than just list the trap, as has been done in the DMG (though with more useful information than prior editions gave traps), I'd like to see the details of the trap given alongside an example to-scale map and images that show the DM what to tell their players that their characters actually see and can interact with that might tip them off to the presence of (and maybe even the function of) the trap without boiling things down to "DC 10 to spot, DC 15 to disable, disadvantage if using a blade instead of thieves' tools, failure triggers trap, [insert damage workings here]" which suggests the resolution is assumed to be done via die rolls even though the lead-up to the examples clearly states otherwise.
Same for terrain and hazards. Rather than focus on just the mechanical bits of them, show examples of how to actually utilize them.
You know, something that actually serves as a how-to for DMs that haven't already figured it out despite the lack, which is still entirely useful to DMs that have already figured it out because it might provoke thoughts not already had.