Blizzard has all kinds of different ways to make a boss hard. One real problem they have is that many of the ways they have to make things hard involve players either being in a particular spot or not being in that spot and ranged classes are drastically better at both those things. Melee classes have tremendous restrictions on where they can be and this translates to a real problem in encounter design.
Last night Wendy and I were talking about how melee are bad in Cataclysm and trying to brainstorm ideas for solving that issue. We wanted to talk about melee advantages and came up with only a few things that melee do better:
1. Unlimited Resources.
2. Immune to antispell attacks such as silence, interrupt, manaburn.
3. Free cleaves.
4. Mobile dps.
The first was supposed to be a limitation that ended up being axed a long time ago. It was obviously terrible for ranged to be just better for the first 5 minutes of a fight, run out of mana and then be garbage after that. It leads to brutal stacking based on fight length. The second has been used here and there but is a fairly gimmicky, fight dependent sort of thing. Ignis in Wrath interrupted casters regularly, which successfully made melee dominant at fighting him and there were several places in TBC and Classic where manaburns were used and which made casters much weaker. The problem is that these mechanics really aren't very good these days. Manaburns don't affect hunters and do affect melee hybrids and interrupts similarly don't affect hunters. Blizzard cannot balance melee by using those sorts of effects. Free cleaves were used liberally in Wrath and ended up being extremely overpowered in some encounters like Anub'Arak and ridiculous in heroics but were often worthless. Blizzard got rid of that as a mechanic and I think they were right to do so. The fourth point is actually useful. On Grobbulus for example the boss has to move long distances fairly constantly and melee can be dpsing him almost the entire time. When ranged have to move to follow him they often lose dps. The issue is that the amount of movement required for ranged to be bad is very large and the mechanic can't be one that forces melee away from the boss or it just ends up being even worse for them.
So given the current model of unlimited resources for all dps, most antispell effects not working properly and free cleaves being gone, what advantage could melee bring to make them worthwhile? My personal favourite is self healing. Specifically in earlier incarnations of WOW Judgement of Light did a lot of healing to the raid and it lightened the healer load considerably. If that sort of effect were available to melee attackers that could make up a lot for the additional damage they are likely to take due to having to be in close. It would have to be something that triggered off melee attacks specifically and probably using a PPM mechanic to avoid rogues just being invincible. It seems a somewhat natural sort of advantage to balance off the penalty of having to eat void zones and explosions and such to continue attacking with limited positioning choices.
Wendy came up with a truly unique solution that won't be implemented but is great to think about. The idea is that melee can continue to attack outside melee range but their attacks grow weaker with distance. Specifically some kind of function that reduces autoattack speed and special attack damage such that at 6 yards nearly full damage is done and at 40 yards zero damage is done would work. The animations would have the character throwing their weapons at the boss and the weapon coming back could signal the timing of the next autoattack - this way the increased distance neatly links the animation with the mechanic. It would mean that melee would be weak at range but they could do reasonable damage while temporarily at range. Obviously since pvp balance would be completely demolished and immersion (for many people, not all) would be very threatened this will never happen, but it is a hilarious idea.