Serious Balance: The Pillar tank was mildy nerfed a year or so back. I feel it really took the 'punch' out of the mid game UEF, especially it's ability to simply punch through any fire-bases (opposed to other factions methods of bypassing, harassing, or outraging them). It also makes the UEF inherently more turtl-ey and less 'on the offensive' (spend less time on T2, rush T3, etc). This makes it in many situations the weakest faction to field as it becomes inherently reactive and not maintaining a presence through the push. FAF really wakes up at T2, no reason to incentive-ize the T3 rush any further.
Fun Change: Cybran ACU, Right Arm 3rd Option - Speed increase, say 0.1 or 0.25 increase in walking speeds. Cybran ACU often lacks fighting or staying power, and is set up to be a little troll or gremlin. While Stealth and Gun or T2 can make it sneaky at plopping down turrets, or cloaking with the Laser, a fun mid-game solution would be the Gun or T2 suite + Stealth + Speed increase. Let the ACE quickly move around / sneak around taking potshots or building things, giving it a high-risk high reward set for mid-game to complement the high-risk high reward nature of the late game laser upgrade.