mearls's idea is not terrible. however, without seeing an actual system, all I'm left with thinking is, "couldn't we just fix the RNG instead?" as he describes it the system feels very clunky and requires metagame knowledge
Under this system, a skill or an ability contains its own DC. Let’s say I have a 16 Dexterity and expert training in that ability. I need to sneak up on a cleric who has a 14 Wisdom and journeyman training. There’s no opposed check. Instead, the active party, the sneaking guy, makes a journeyman Dexterity check. My expert training wins, meaning that I can sneak up on the cleric. so wait the cleric doesn't even get a spot check now?
However, let’s now say that the cleric is suspicious of being followed. He takes a moment to scan the area and make a Wisdom check. That check’s DC is matched against my expert Dexterity. He is one rank below me, so he needs to make a DC 20 Wisdom check to notice me. so you have to cross-reference the difference between the characters to know the actual DC rather than simply making an opposed check. rolling a +12 for the elite assassin vs. the +4 of the novice cleric seems a lot easier to me imo
Let’s assume that I’m playing a rogue and I’m tracking the cleric in a shadowy ruin. The cleric, suspecting that he’s being followed, casts a light spell down the hallway where I’m lurking before he makes his check. The DM can then drop the DC down one level, to journeyman. The cleric’s target number is now 10. Just as in the system described last week, players (and DMs) are encouraged to engage with the game setting and come up with ways to tilt the odds in their favor. so we're supposed to tell the players that they're going to autofail so that they engage with the system?
okay so how does this even work. why do we have varying DCs and cross-referencing stats and it sounds like you're going to have to say "well the rogue has +1 skill levels on you so he automatically wins, you had better do something to make it easier to spot him" and what happens if the rogue fails his first stealth check then? does the cleric automatically spot him or what?
yet another problem: what about tracking NPCs. the 4e skill system is quick and easy, and I would love it if the skill list weren't neutered and the RNG was a little more solid. since I'm the kind of guy who like statting up NPCs using PC classes (I'm aware this is a no-no in 4e) it makes dealing with them much easier than using the 3e skill system. with the skill tag system, I can easily calculate a skill number on the fly and not have to worry about anything--just roll an opposed check and see if the monster spots you. with this system however, we're looking at a bunch of extra, behind-the-scenes math which works well when you have everything planned out exactly in advance. but what happens if the PCs are trying to follow an NPC that isn't statted up? using the 4e example, if they were trying to follow a ranger, I'd say "okay he's around level four with a 16 Wis and trained in perception, so he's going to have a 5 + 2 + 4 = +11 perception modifier, make your roll" (I'm aware they have a system for passive perception but I dislike that). with this system I have to decide his wisdom modifier and his specific level of training and then recalculate the DCs based on that
like all mearls ideas this one has promise but lacks execution. also I'm sensing a bit of FUDGE/SotC in this system where you're rolling your "extraordinary" stealth or whatever vs. the "average" spot check of the cleric.
imo if mearls wanted to do this right he would do something like the following (using the rogue vs. cleric example):
1. the rogue makes a stealth check. does he succeed? IF YES: he follows the cleric because his skill level is so high. IF NO: his skill level drops by one for the encounter; proceed to step two.
2. is the rogue's skill training now equal to the cleric's? IF YES: make an opposed roll using the normal rules and proceed to step three. IF NO: return to step one.
3. who won the opposed roll? ROGUE: sneak successful. CLERIC: notices the rogue.
obviously this is far more complicated than simply making an opposed roll but if mearls wants this weird kind of granularity then so be it.
alternatively what I might do is give characters a number of "training bonuses" for their skill training (untrained has zero, basic training has two, expert training has four, etc.). at the start of each encounter, these pools refresh and allow them to reroll their skill checks or perform special abilities, each one taking a certain number of bonuses (for instance a sneak attack might take two points where hide in plain sight might take three or more). obviously this wouldn't really work for the D&D system as-is but it's just a thought