Wrath bought a return to the fabled hero class with the announcement of death knights. Trumpeted as the first hero class, they would get a unique and epic storyline and begin their journey at level 55, immediately making them "more powerful" than their predecessors.
This has bought the expectation from some that that burst of power should last. If the original Warcraft III hero units were head and shoulders above other units, shouldn't hero classes be the same? To be fair, this was arguably (if unintentionally) true for much of the early weeks and months of Wrath. Blizzard was experimenting with adding a new class for the first time in the game, and they certainly erred on the side of giving us a lot of cool toys and powerful mechanics.
By the middle of Wrath, though, they'd found their footing and bought us back down to earth, and now we reside on the same buff and nerf roller coaster that every other class abides on, and we currently sit somewhere in the low middle on DPS charts and have a solid but not invincible tank spec.
And that is honestly about where we should stay. There's arguments for buffs to be made, sure, but we should stay in balance with the other classes. Hero units worked in Warcraft III because everyone got them. Everyone had that extra spike of power on their side in a given match. In WoW, it's different. You have your main character, and your character has a certain level of power, and that's all. You simply can't make a single class more powerful, even if they bear the moniker "hero," because it is unfair to people who don't play them.
As it is, we need to accept (and most death knights have accepted, mind you) that hero class does not mean overpowered. It means that it has a special, "epic" origin and starts at a higher level. As it is, Blizzard hasn't rushed back to the hero class archetype, making monks a normal class who share their race's default starting zone and start at level 1. While Blizzard hasn't ruled out making new heroic classes in the future, we may end up being unique in this regard. Our heroic origin will have to suffice, and our skills will have to make up the rest.
The unholy intellectual and intellect plate
In the era of gear consolidation, one spec reigns supreme. While large groups of other classes scramble for the same drops off each mob, holy paladins have exclusive dibs on any plate armor with intellect on it, because no other plate class or spec gets any benefit from it. This is certainly something the devs have noticed, and while Ghostcrawler has said they're not completely happy with it, it's not something they can easily fix either.
One of the most community suggested fixes for this conundrum, especially among death knights, is to convert unholy death knights to use intellect plate. The argument for this revolves around the idea that unholy is essentially the "caster spec" of death knights, with diseases and the Death Coil "nuke" serving as huge sources of damage, along with a pet ghoul. It also adds the possible bonus of enticing more people back to the somewhat underplayed unholy spec with the prospect of far less competition for gear.
There's a few reasons why this isn't something that will happen any time soon. The biggest reason, probably, is that unholy death knights remain, despite their "caster-like" bells and whistles, essentially a melee DPS class. Melee strikes are still a very central part of the unholy damage rotation. Thus, in order to switch us over to a caster spec completely, you'd have to either remove the melee portion altogether, or bend over backwards to keep it in place.
You could, in theory, solve it by converting intellect to strength similar to how spell DPS hybrids currently convert spirit to hit rating. That said, Ghostcrawler has indicated in the past they find that design inelegant and unintuitive, and would rather not reuse it. In addition, that would require either the design of unique spell power weapons for use in melee combat, or that strength remain a viable stat for unholy death knights, which brings us back to square one. It's also worth noting that enhancement shamans used spell power weapons for DPS for a time, and Blizzard did their best to squelch that.
So in short, converting unholy death knights to intellect plate might cause more problems than it solves, and ultimately, might not even solve many problems. After all, unholy death knights would still have to compete for the same tier armor tokens as always. In short, it would be too much work for a dubious reward.
The rune blade as icon
The idea of a rune blade as iconic to a death knight began with the Warcraft III hero class, and most specifically with Arthas, who marked his descent into madness with Frostmourne, the first and most iconic rune blade. PC death knights get a little bit of this experience with their own rune blade from the death knight starting zone.
Alas, that rune blade quickly falls by the wayside, as you upgrade to bigger and better weapons. Some death knights have suggested that we should have our rune blades back, whether it be from converting Runeforging to a whole new ability that actively creates and upgrades a rune blade, or via a legendary quest line that allows us our own special weapon. To these death knights, the rune blade is such an iconic part of the class that it deserves special consideration at all levels of play.
The biggest argument against this is that Blizzard has just plain cut back on class-specific content. Epic mount quests for paladins and warlocks are gone, as well as epic flight for druids. While they made an exception for rogues in Cataclysm, for the most part, Blizzard tends to prefer than large, epic quest chains be completable by as many characters as possible.
Now mind you, I am a big fan of class specific quests. I finished the druid epic flight form quest as well as the warlock and horde paladin epic mount quests before they were removed, and I loved them. I think there should be more class quests like those, that involve class specific lore and multiple steps full of interesting mechanics and battles. But Blizzard doesn't want to spend the development time on them for the most part.
The other argument is that it just wouldn't be a compelling mechanic. As someone who played a druid main until Wrath, one of the most frustrating things for me was getting an awesome new staff and knowing it would be hidden behind a shapeshifted form most of the time. Having the same blade graphic at all times as the rune blade overrode any other possible graphic would get just as old, I'm sure.
In addition, right now, weapons upgrades are one of the hugest ways DPS death knights mark an increase in power. Forcing death knights into a single rune blade could take that part of the class away. Essentially, if we were forced into using a class-specific rune blade, we'd find either that we didn't upgrade fast enough, and felt behind other classes, or we upgraded too quickly and easily, unfairly outpacing other physical DPS classes. You could, in theory, solve this by making the rune blade non-mandatory, but then it would just be a case where death knights would completely abandon it whenever it was too underpowered.
The final point to make here is that technically, we have a solution. With transmogrification, you can use your old rune blade from the starting zone. In patch 5.2, if the planned transmogrification changes go through, it'll be even easier, since even a mace or axe can turn into a sword. This does still leave dual wielders lacking a bit, but otherwise, it does at least provide an alternate avenue for those who can't bear to part with their rune blade.
Learn the ropes of endgame play with WoW Insider's DK 101 guide. Make yourself invaluable to your raid group with Mind Freeze and other interrupts, gear up with pre-heroic DPS gear or pre-heroic tank gear, and plot your path to tier 11/valor point DPS gear.