Traits are characteristics of a card that include power, toughness, and skill. Templating will have to be modified to include the new traits. Ideally each trait is represented by a symbol on the card and in rules texts. For instance, an ability that says "Target creature gets +1 [Power symbol]" instead of "gets +1/+0". Then +1/+1 and -1/-1 counters would be replaced by +1 and -1 trait counters, respectively, and they affect all traits. It can be simplified to something like "Put a +1 trait counter on target creature", and all traits will be raised respectively.

Skill is a variable for abilities. For instance, absorb can be assigned as Absorb [Skill symbol]. That means the absorb ability is always updated when skill is increased or decreased.

That's... actually a really interesting idea. We brainstormed a few possible ideas for what could be the "third number" in the P/T box back when Challenge # 019 happened. But none of the ideas were as interesting as this one.

So the idea is that, say, Battle-Mad Ronin would be a 1/1/2 with "Bushido [S]"; Craw Giant would be a 6/4/2 with "Rampage [S]"; Mycoloth is a 4/4/2 with "Devour [S]"; Kozilek, Butcher of Truth is a 12/12/4 with "Annihilator [S]" (and maybe also "cantrip [S]"), and so on? Probably most creatures without an ability that cares about skill would have default skill 1 (maybe tokens have default skill 0). Granting bushido and other skill abilities becomes more interesting because creatures with a high skill for some ability are also good targets for granting other skill abilities. And once you have enough cards that grant skill abilities, you can have "vanilla skilled" creatures like a vanilla 3/3/3 for , just begging to be taught bushido, or absorb, or frenzy, or one of the as-yet-undesigned keyword abilities that would naturally emerge once you had the skill symbol [S] to use in them...

Yeah, I really like this!

Chunk of complexity; and hard to back-port, would cause a chunk of short-term pain.

But it's an interesting knob to twiddle. Are there cards (many cards) with multiple skills of different sizes?

It's also a really obvious nice target for nerf spells. "Target creature has 0 skill"

This is another idea that'd make more sense if being introduced from scratch in a reimagining of Magic, or an alternate-universe Magic being designed from the ground up knowing what we know now. That'd mean we could also apply it to flanking, battle cry and exalted, as well as those where it fits more naturally like some or all of fading, vanishing, amplify, soulshift, dredge, bloodthirst, graft, ripple, reinforce and modular. (Hm, although some of those can be on auras like Reality Acid or instants like Darkblast and Surging Flame.)

Kinda odd comparing vanishing and suspend - high skill is good for one, and low for the other.