I can see the marketing now: "A world rich with interaction between new players and veterans sharing their knowledge!" This sounds great, of course. Up to a point.
Have you ever noticed how high school physics classes rarely take place at Fermilab? Or how rarely you see brilliant physicists sitting in high schools listening to the teacher stumble his way through the concept of an equal and opposite force? This is segregation. Self-segregation. There are distinct areas and groups and people separate themselves among them. Veterans go here, students go here.
At this time I think that's the greatest weakness of WoW. It mixes the players too much. We cannot easily self-segregate into appropriate groups. This leads to problems. What problems?
The noob in your heroic. Or, the eltist jackass in your heroic.
People in groups should be of about the same experience level, of about the same skill, with about the same gear, and about the same goals. In this situation no one is being carried and everyone is inclined to work together because they have shared goals, or at least compatible goals. Anyone still learning is not wasting time because they're all still learning, and can learn from the mistakes of the others.
Leveling instances do a decent job of this. While they do mix veteran alts and new players, they are at least of similar gear and level. At lower levels veteran players may be more inclined to be patient, being able to believe that they are playing with new players who are 'allowed' to be still learning, rather than noobs who have been 85 for who knows how long and are still awful so let's call them noobs and call it day. You won't see many level 85 characters in your Stockades run berating you for being carried.
How would we get this player segregation? Well, let's look at what leveling is: linear. Linear content naturally separates players. A level 10 has played less than a level 20, unless the level 20 is a speed-leveled alt, in which case he's probably still played more, just not on that character, so it still works.
Get rid of all this "we want players to see content" crap. It's not working out so well. It's fundamentally incompatible with challenging content and good community. If player misses raid Z, but they are able to actually enjoy raids X and Y, I think that's better than stumbling through raids X, Y, and Z half-seeing the content and getting blamed for everything.
Bring back linear raiding.
While we're at it, bring back linear heroics. Linear heroics? Well sure. Let's not pretend that Mechanar and Arcatraz were of the same difficulty. Were they perfectly linear? Not at all. But there was some known gradient of difficulty. There is in Cataclysm, and there was in LK heroics as well, but those have the random dungeon problem. If people are not picking their instance, they're also not picking their difficulty level. Someone who queues for Mechanar is there for easy quick badges while someone who queues for Arcatraz is there for harder badges and maybe a raid attunement.
Linear content naturally separates players. This isn't a bad thing. It puts players with their peers. When people know they are more or less equal, they're not such dicks about everything. Contrast that with the current system which vaguely pretend we're all equal, when we're clearly not, so conflict arises.
This also means that heroics cannot be the elevator that they are now. That use of them pushes players who have long outgeared them back in, and int conflict with the newer players, or players who aren't good enough to play past heroics.
I expect that merely by putting players with others of the same experience and power level, many of the LFD problems could be reduced. I see the ideal tool as a mix of the BC system, pick a few and people can see you, and the LK system, randomly random with randoms. We'd pick the heroics that we think are suitable for us and then be put in a random one of those. But no random dungeon bonus reward. I think a system where people are doing appropriate level content, in terms of challenge and reward, could lead to a better community, even with cross-server. In fact, since this is likely to reduce the pool slightly, by removing the more advanced players and slightly separating the rest, the cross-server function may be necessary.
To clarify, I don't think we should return to the almost perfectly linear raid structure of vanilla. That was a problem. For starters, I'd have two raids per tier, at least, so that there are no gatekeeper, guild-killer bosses. Major challenges are great, but when a guild is stuck one one single boss for months, with no real alternative content, that's a great way to make people not want to play. Even if the alternative content won't help get past the gatekeeper, it can at least offer an alternative activity to break up the potential monotony.
I'm sure this won't be a popular idea. And I'm sure "come back and do it in a higher level group next expansion" isn't much consolation, since it won't be the same. But consider this: if you're playing trivialized content endlessly with players who are sick of being there, it also won't be the same. Or, perhaps it will be the same. Even worse, while the progressive badge/point structure gets people into the last raids, it also means newcomers miss the first raids, since everyone has moved past them. Wouldn't it make more sense to have veterans in the latest raids with other veterans, new players in the older raids with other new players, and not have the constant conflict between skill and dedication levels?
There will, of course, still be the alts and rerolls going through, veterans in with new players, but that will be the exception rather than the rule.
So if you're sick of playing with noobs, give this idea try. And if you're sick of playing with elitists, give it a try as well.
P.S. Do not relate this to real-life segregation, beyond the example I used.