1) Good article. I love traps, and find this is a good supplement to the DMG overall.
I'm also a lover of traps

and frequently looking for ways to make them run better for my group. I think this article is a good start and shows they're thinking about traps a bit, but they have a long way to go.
3) I am not sure if "I use my thieves tools to disable the trap" should always be considered too vague. When the warrior says, "I hit it with my sword" we don't always say, "Precisely how?" thought we might on occasion. Shouldn't the rogue sometimes be able to just say, "I disarm it with my thieves tools?"
You're making me think about trap typologies. For example, monsters have different types (e.g. construct, fey, fiend, etc), and those types have common traits which influence how a warrior might go about dealing with them. For example: silver for lycanthropes and fiends, adamantine for constructs, douse trolls with fire, etc.
Maybe there's a translation of "monster types" that can apply to "trap types" that can help clarify when "I disarm it with my thieves' tools" is a possible course of action.
But that's also the endpoint of the trap – it's the killing blow against a monster.
The
interesting stuff is mostly leading up to that point of attempted disarm – for example, realizing there's a trap thanks to pattern recognition / intuition / experience, avoiding triggering it, and figuring out how the trap works.
4) While passive perception should be the default to spot a trap, Investigation might well be used when a player says, "I am curious about this desk. I will carefully examine it for traps." Indeed, the difference in Countermeasure descriptions for the Falling Gate trap and the Fiery Blast trap give me the impression the author isn't sure how to differentiate between Investigation and Perception sometimes - both traps use a pressure plate, so why include Perception to spot one and Investigation to spot the other when that portion is essentially identical? I think more traps should include entries for both in the Countermeasures section.
I've thought about this, and I have what may be an unpopular (or at least un-modern) perspective: For
most traps, Perception (whether passive or active) should NEVER obviously identity the presence of the trap. In fact, no check should be involved.
"It's a trap" should rarely be a simple matter of sensory perception, but of internal realization. There are details a perceptive character can gather about the environment/situation, of course, but at no point in responding to a Perception check (or passive Perception) should the DM say "you notice a pressure plate." Maybe the exception to this principle is the tripwire triggered trap – maybe that sort of trap is the kind where Perception really matters, because once you see a tripwire that's a dead giveaway of the presence of a trap. And maybe those Perception-critical type tripwire traps are associated with kobolds and goblins.
Let's take the pit trap in the UA article as an example.
That pit trap is covered with a camouflaged canvas. It's screaming "I'm a trap!" There's no cleverness involved, either on the part of the trap maker or the players. The design of the trap necessitates a rather dull dice roll (or comparing two static numbers). It's dull because there's no real decision point in encountering the pit trap as written. There's a canvas? Nope, you didn't notice the canvas, sorry, you fall and take damage. :/ There's a canvas? Yep! OK, I look under it. It's a pit trap. Well, I'll walk around it. Congratulations for figuring out that very challenging trap; you skirt around the edge without issue. OK, what was the point of that? :/
But in my mind, the fun of
most traps is in how they make you puzzle them over, figuring out how to solve that unique trap, devising creative ways to interact with it. And that means a trap should present players with interesting choices/dilemmas.
In my re-write of the pit trap, I got rid of the obvious canvas and instead use brittle stone masked to appear just like the surrounding stone (if False Appearance can flawlessly pass off a galeb duhr as a boulder, then I don't think it's too much to expect traps to operate the same way). Perception in this case isn't about noticing a camouflaged canvas whose presence would scream "look out, I'm likely a trap." Instead, I had scuffing around the edges of the brittle stone, which is the ledge monsters walk around the trap and where the monsters replace the brittle stone after the pit trap is triggered. PCs noticing that then have a couple decision points:
- First, do we think this could be a trap? A camouflaged canvas is kind of a dead giveaway. This, not so much.
- Second, which section do we think is dangerous, the scuffed edges or the un-scuffed middle? The canvas removes any ambiguity about what's being hidden (obviously, it's whatever is under the canvas!), but this reintroduces ambiguity.