I had a few things I was hoping for that never got in the game:
1) Optional Knockback. They made the run speed part of Speed Boost optional, so why not give us an option to turn knockback into simple knockdown? Sure, any enemy with one full point of knockback resistance would ignore your knockdown attempts, but then I could play any of the numerous knockback-heavy powersets and not have quite so much trouble with all the scatter it causes teammates.
2) The next issue. They had some pretty sweet new powersets, not to mention upgrades to the old power pool powers, all in the works. I doubt that'll happen now, though. *shrug*
3) Challenge/Threat fixes for Scrappers. This one is a bit more out there, but here's the thing: Scrappers are DPS, not tertiary tanks. If you want a primary tank, you get a Tanker. If you want a secondary tank with some nice DPS, get a Brute. Why, then, did Scrappers have a 50% increase in threat generation built into the characters? The Real Numbers stuff revealed that strange phenomenon, and I suspect it was a holdout from before defensive sets got nerfed so bad in the early issues. At the very least, it didn't really fit once anyone could play any archetype on any side (sans epic ATs). Usually it's not a big issue, although I never could meet a tanker who could hold aggro off of my titan weapon/electric armor scrapper later on. Challenge, though, was pretty rarely used. I'm sure someone somewhere used it, but honestly, it's just faster to kill someone who's aggro'd on your support-based pals than to taunt them. It did make for a nice excuse to skip a power though lol.
4) Archvillain fixes. Before end-game was all about incarnate trials, the wacky rules of Archvillains, Heroes, Monsters, and Giant Monsters weren't really that bad. I mean, at least there were plenty of other enemies to fight, and even giant monsters weren't that bad. Specifically, I'm talking about both the insane immunity to control powers (I really feel for you controllers and dominators), and the 90% resistance to debuffs thing. I understand it, but it also applied to certain buffs. For example, a defense-capped scrapper ran at 45% defense, which mathematically translated into taking 90% less hits. Since having defense counts as debuffing the enemy's accuracy, archvillains ignored 90% of your defense (not resistance). This meant that your vaunted 90% mitigation is now a measly 9% mitigation. The total incoming dps would thus be raised from 10% to 81%, a total boost of 710% more damage. Ouch? Surely there's a better method out there somewhere. Too late now, I guess.