There are RTGs, yes, but they are only slightly better than Solar Panels. They are single-block "set and forget" passive power. As for nuclear becoming more interesting, that's only because it's solving a problem that IC2 created with its new machines that require more power, but the purpose of those machines is not substantially different than the original IC2 machines : they process stuff. Same story, just different actors.
A, while UU-matter is now more involved and there is at least a liquid you can look at, the result is still the same. Energy gets converted into matter. Nothing really new there, either, just more mechanics for the same result.
Rather than focusing inward and creating solutions to self-created problems, IC2 would be better served if it worked more closely with other, major mods, to fill in the gaps and provide better interfaces. Teleporters, TE Tesseracting, Ender Storage bags and chests, Ender I/O, tools from various mods, OpenPeripherals, TC golems, much of MFR, the entire AE mod, food/crops, and anything to do with bees are great examples.
How about an IC2 robot that would be a cross between a CC Turtle and a Golem ?
How about an IC2 teleporting train track ? That would provide a nifty alternative to Ender Chests and Item Tesseracts and make TC, RC rails, and SC2 more attractive.
How about IC2 levitators that can be placed under blocks and slowly move them ?
Lots of interesting things that could have and can still be done.