Well, I almost never post, but I'll give my two bits.

For a hypothetical 5e, I'd like to see a more
streamlined version of 3e, especially in regards to generating stat blocks for NPCs. That would make my life easier as a DM.
I also feel compelled to mention that I don't really know what to do with 4e. It's a weird game, and I can't truthfully classify it as D&D. That's troubling to me. The reason I say this, is that D&D players normally expect a
shared experience when discussing D&D. Whether you started playing D&D in 1977 or 2007, you could expect the following:
* There was a planar cosmology with Prime Material Planes, Inner Planes, Outer Planes, the Ethereal Plane, and the Astral Plane.
* As PCs went up in level, they rolled a die for Hit Points (d4, d6, d8, etc.).
* There were mooks that had approximately 1 Hit Dice (Orcs, Goblins, etc.).
* Ogres were huge brutes with approximately 4 Hit Dice.
* The magical fabric of the universe was very precise, with 9 levels of spells.
*
Magic Missile was a 1st-level spell, and it automatically hit, unless countered by a
Shield spell.
*
Charm Person was a 1st-level spell, and it transformed the victim into a buddy or a slave.
*
Fireball and
Lightning Bolt were both 3rd-level spells that inflicted d6 damage per level.
*
Teleport was a 5th-level spell...with a chance of mishap.
* Non-combat magic was as prevalent as combat magic.
* If you were badly injured, you needed to either rest for many days or procure magical healing.
* Clerics are healbots.
* Rogues or Thieves probably steal things.
* Saving Throws improved as you went up in level.
* For better or for worse, level draining existed.
* Your character's Alignment could influence what he did for a living. After all, Paladins do not grow on trees...

* A character could (in game mechanics) be as defined by his flaws as by his strengths.
There are many more details the various editions have in common, but I figured that I'd just throw a few of them out there.
Individually, these details might seem to mean very little on the surface, but
collectively....these little details create an implied meta-setting, and add up to a
shared experience that D&D gamers have come to expect for
decades.
Now....the problem many people have with 4e, is that it took that shared experience of the other editions, and chucked it clean out the window. As a result, the D&D fan base is far more fragmented than ever before. It's so completely fragmented now, that three years after the release of 4e, the 3.x fan base remains as large as the 4.x fan base, and in fact might be considerably larger. Before anyone scoffs at that statement, let's remember that
Pathfinder alone is challenging 4e in the marketplace. If we compare the two fan bases...
* 3.x (3.0, 3.5, Pathfinder, d20/OGL games [like Castles & Crusades, Trailblazer, and Fantasycraft], D&D Online, Neverwinter Nights 1 and 2, playing online via some type of MapTools program, etc.)
* 4.x (original 4e, "errata'd" 4e, Essentials, Gamma World/D&D, playing 4.x online with some form of MapTools program, etc.)
...then we see that that the 3.x group is probably a larger gaming segment. What that means in the long term though, is anyone's guess, as I don't really believe that WoTC can simultaneously placate both the 3.x and 4.x groups. But who knows? Maybe WoTC could surprise us all, and create a design that could "wow" all of us. Stranger things have happened...
Many regards,
the Sacrificial Lamb