I still love the idea of maintaining and improving the original Gundam, given how much of a symbol it is. I know Zeta Gundam-era technology vastly outdated it, but I have fun musing on the kind of psychological effect that a recognizable but modified RX-78 would have it if showed up in the middle of a fight and started blowing Titan or Zeon remnant forces to smithereens. :D
Even though it's from the Build series instead of UC, I think it's worth mentioning the GPB-X78-30 Forever Gundam. A full armour RX-78-2 with psycommu weaponry. Its aesthetics fit very well with UC.