Look, by any defensible definition of 'diegetic' there can be NO game mechanics who's operation by a player fits that bill. That's my conclusion. Rolling dice is not diegetic (aside from your peculiar case, perhaps), marking off hit points of damage is not diegetic, no forms of manipulation of a currency are diegetic, etc.
And this is why I consider digetic/non-digetic utterly irrelevant to a game. From where I sit, almost no mechanics are known the the
characters, except in some pretty in your face requirements. The odds of those mechanics might be, but it doesn't matter. Such as Jonny Archer knows that he can hit a man sized target about half the time at 100yd, and a walking one to 60yd... He doesn't know that the decision is made by a being rolling an icosahedron with 20 numbers on it... nor his THAC-0 is some specific number. He knows only the outcomes of the mechanics, not the mechanics themselves.
So D&D wizards, given that spells fall into ranks, and until you can cast 3 spells a day, you can't learn the second tier spells... guilds would require a demonstration for access to the spellbooks of the guild of ability to learn it before trusting you to study it from the tutorial book, get it in your brain, then intersect it with your spell book meaningfully to you, and apply the magic goodies at the intersections to inscribe it in... Especially since accidental casting of the spell from the book directly results in both books lacking the spell... (then someone has to go and re-add it to the instruction copy...
But in the end, digetic or non doesn't affect how I run, nor how most of my players play; it's far less relevant than the player's choices being reasonably informed.
Except they don't overall make the situation worse unless you are playing badly. They overall make it better - but at the rate of two steps forward and one step back rather than always going forward cause we can't find reverse.
Which, for many, myself included, sounds absolutely «bleep» «bleep» totally «bleep»ing miserable a way to spend an evening.
I don't care IAB episodes in cop shows, either, unless IAB are the main cast. (cue BBC's
Line of Duty about AC-12)
Just, like, use your imagination, guys.
Much as I allow use of techniques for retroactively bringing things, I genuinely dislike them. It's not a lack of imagination, it's that I now have to reimagine the inbetween... and that some players use it to avoid Encumbrance penalties... Cue Shinobu and her extridimensional pocket hammer, and ability to partially manifest extracorporally via phone line... it's funny in the visual medium, but not something I want happening in games without everyone being both into and capable of such.
One of my friends called the Destiny Point spend "Quantum Rocket Launcher" ... especially after I docked his character's credits for the cost of said weapon.... I let him have it on the spot, tho'.
I usually have a fairly decent mental view of things... much better than most of my players... I don't use meeples for myself; I use them for my players; a way to reduce arguments. Using abstracted tokens like meeples also reduces the misconceptions about what's what - since it's abstract, they're going to ask if they don't remember, not assume it matches the mini.