Obryn, why can't "marking" be achieved as a maneuver? You use your reaction to swing at the guy if he attacks somebody else than you, and your swing is distracting too, thus giving him a -2 to hit your ally. There are already a few maneuvers like that. If he attacks you, use your reaction to parry him. If he attacks your friend, essentially get an attack of opportunity on him. There's nothing in there that requires magical or narrative suspension of disbelief. Sure, you only get one reaction per round, but it refreshes at the end of your turn.
Maneuvers are pretty much universally loved from what I've seen. Makes fighters fun to play (and actually somewhat similar to the 4e fighter, but still more realistic and constrained)
It depends mostly on how it's handled, honestly. There was a thread about Fighters getting nice things a few months ago, and I didn't see anything that lived up to what the Fighter can do in 4e by default. So I wasn't impressed, but that's not to say it's impossible.
Marking is one mechanical implementation of a theme. There are other possibilities on how to represent it in play. But for the record, neither "realistic" nor "constrained" are on my priority list for a new D&D.
Through the use of rules modules? Extremely likely. But I would agree with previous posters in this thread who have said that the "metagame" module needs to be separate from the tactical module. I didn't really understand what they were saying until now, but yeah, if marking is a "metagame" ability, fook that sheet, my man.
Marking is less "metagame" than, say, bennies/action points/fate points, but yeah, it's definitely in the metagame space.
I'm thinking that a "module" for this sort of thing would really amount to "whole 'nother game," and that's where I'm running into a wall on the topic.
But look, lest there be any doubt, I want 5e to be the best 5e that 5e can be. I don't want it to be another 4e, since it's clearly not going to be any sort of "4.5"

. But I
also don't want it to be another 1e, 2e, 3e, or some unholy conglomeration of the lot. I don't want it stuck in any mechanics or assumptions that other, perfectly workable editions of D&D are better at. Quite seriously, the only way Next can win me as a customer is to do something new, radical, and different that I haven't seen in D&D before. I acknowledge - this may be impossible without alienating much of the rest of the fan base, but that's where I am. I'm okay being "left behind"; much like I said 5 years ago, it's not like WotC's coming to my house and burning my books. (Note - this last packet is the first evidence I've seen that Next is developing towards being its own thing rather than some kind of reheated D&D mash. At this point, it might get to be a game in the rotation, though probably not my weekly game.)
Tying it back to the topic (or at least the derail): As far as metagame mechanics go, the games I love vary wildly in their implementation, but I've found that - down the line - the ones I
really like nowadays and
really want to run tend to be heavier on the metagame side. Far from being lazy, I see this as elegant, simple, and clean - focused on the effects rather than the process. Case in point... I
love Earthdawn. It's about the most "associated" game you can imagine, with essentially no metagame whatsoever. Really - every mechanic from spells to experience to hit points to karma has an in-world, character-observable justification. It manages to do this while letting "martial" characters be awesome (through...er...giving them magic, but whatever). But, when it comes down to it, there's
no way I'm going to run it because in getting to that point it's become
super damn complicated.
So that's why I'm a big proponent of the metagame's inclusion, here, and why we're going down this narrative tangent.

If Next isn't that sort of game, it's a lot less likely to win me as a customer ... because I already have quite a few perfectly playable editions of D&D that are on the "low metagame" scale and I'd run them in a heartbeat. (Behind 4e, AD&D 1e and RC/BX/BECMI are my favorites; I'd like to run 1e again, but with two young boys, there just isn't the time.)
OK. /ramble. Time for some Bioshock.
-O