This is why I hate popular terminology. I wouldn't call those things metagame elements -- they're abstractions, to be sure, but anyone wearing chainmail has an "armor class," even in the real world. It is harder to injure them than it is someone in plain clothes, even if the calculations of how much harder it is don't fit a neat linear scale.
Similarly, class, level, experience points, and hit points are /terrible/ approximations of real-world concepts, but they are reasonable compromises when you consider the unwelcome complexity of actually tracking the aspects of character they represent. To play D&D is to accept these half-truths -- the game embraces them with consistency as the core of the simulation. Put another way: they are the game itself, not the metagame.
Metagame kicks in, for me, when something happens because the rules say so, without the benefit of internal consistency. Magic happens by fiat, but the fiction allows for it so it is okay. By contrast, marking also happens by fiat, but if I were trying to goad a similarly focused (but non-violent) response to myself outside of combat, even in D&D4 that would require a skill check. Why can I "mark" someone in combat without even the need to touch them with my weapon, but have to make a skill check to goad someone outside of combat? More simply, why is there one set of rules for combat and another for peace?
If there's one thing I definitely must see in a tactical rules module for D&D5, it's that it must be internally consistent with the non-combat rules (aha, on topic!).
I guess 'internal consistency' might be what some people mean when they say 'verisimilitude?' It's not really what it means.
Class, level, and experience are abstractions, but they're abstractions that take place outside of the action. It's off to the side where you don't see it at play. And they're very much conventions and necessary abstractions.
Hitpoints and Armour Class are the weird abstractions that each DM grapples with in their own way. Some accept the abstraction, some just ignore them, some just try not to draw attention to the abstraction, some just don't care.
Marking is a new one. But unlike other abstractions which represent a real thing in an abstract way (representing health, increasing skill, the protection of armour, an associated suite of skills) marking seems first and foremost to be a mechanic. It's not really an abstraction of anything, it's just abstract.
It's the equivalent of the threat/hate meters in most MMOs, but simplified because tracking a percentage is unneeded bookkeeping. Which are necessary in an MMO (or any multiplayer game) because the game needs some way for the AI to pick which target to attack. But these are unneeded in a tabletop RPG because the game is run by a DM who can decided for the monster, who the largest threat is, and choose variably based on the monster's intelligence: attacking the creature doing the most damage, the creature to hit it most recently, the nearest opponent, a certain race or class, or the most tactically sound target.
There's also the side intent: it denotes the ability of a defender to draw aggro. Because a problem with tanks in earlier editions was their inability to prevent an opponent from just walking around them to flatten the wizard.
However, this is a very mechanical problem, because there's very little to actually prevent an opponent in a real fight from dashing away from the heavy to attack the healer. You can see this a lot in role based FPS (Team Fortress comes to mind) or even in football: you can't just outright stop someone pulling away to go after the doctor/quarterback, but you can stand between them and make it difficult. Drawing aggro in MMOs is really a crutch for those games' inability to have a character block passage (as having toons unable to pass through each other causes even larger problems).
Getting past the intent and abstraction marks kinda sorta reflects the defender's ability to interfere with the attacks of an enemy, but it does so extremely poorly as you can mark someone you can't attack (the dragonborn breath weapon or fighter with a javelin), and marks don't go away if stunned, held, blinded, etc.
It also often reflects taunting, or an enemy's attention becoming focused, which is even more odd ("I have enraged the enemy so much it really wants to attack me... so it takes a penalty when attacking anyone else.")
More often than not, the story marking is trying to tell does not match the mechanics. It's a very simple expression of a couple opposing ideas. And simplicity & elegance certainly have their place in the rules. But I think marking is a little too simplistic. It tries to do too much.
I'll be very happy not to see marking show up again, and instead see more specific expressions of the rules. Such as fighters just being able to burn a reaction to attack an adjacent foe hitting an ally, or paladins using channel divinity to Challenge someone, or a taunt power that grants enemies a bonus to hit the taunter.