Seeing as the new technic allows for custom packs, I would see quite a few mods in:
1. Redpower Wiring/logics (the automation would overlap assembly line if we took it, so just the redstone upgrade is good)
2. Possibly Optifine for the client-side
3. Smart Moving could be nice
4. Sometimes seen as hacking, TreeCapitator
5. SecretRoom and SoulShards looked like nice stuff
6. Simple but cool, Rotten Flesh to Leather (pretty sure you can make higher the ratio of rotten flesh/leather)
7. I would have proposed the Liquid Metal, but it a buildcraft addon, probably cannot be made for UE
8. Possibly Powercrystal's Powerconverter if you intend to put any other mods (can also be used from UE to Railcraft)
9. NETHER ORES !!! (from PowerCrystal too) Am I the only fan of nether mining ? well, this is my jewel, my dream, my eternal friend !
10. FlatBedrock is nice for underground building (I like PowerCrystal's mods, alright ?)
11. You could get his minefactory, but I guess it would overlap too much on UE....
12. Better Anvil, because a max level sucks
For now my list is pretty much done, but I might think of some others in a near future.
PS: The new launcher doesn't allow for manual choice of version, so the server is currently unplayable using the new launcher.
Edit1: Now that I think of it, PowerConverter allows you to have like any sort of machine you want, as long as you disable the generation from other mods: (i.e.) You can put IC2 in, but remove the generator (which would concequently make the other energy generation of IC2 impossible, you would have to transform it from UE) I know the answer would be no, but I am just saying...