remove all metals and ores and gems from tekkit
replace with TFC stuff
yay
Tekkit's other big failing is that it's actually a bunch of other mods and they often double up on things.
Redpower's Blulectricity vs IC2 electrics, Redpower Computer vs ComputerCraft
In the first case I'd like to see it cut entirely (I love frame motors but I hate having to lay all the different cables, not to mention the solar panel seems to be the only blulectric generator? I'd prefer the option to just not include it, given that the official explanation for redstone is literally "magic" last I saw) and in the second case, ComputerCraft wins out simply by not being a super low level wank-fest. It implements a simple to use language and doesn't make you forget about with hardware. It's about getting stuff done. RP2 Computer is just overcomplicating the matter.
Really though it wouldn't make sense to combine TFC/Tekkit. TFC is focused on the more primitive tech, the medieval/fantasy survival aspect. Tekkit stuff is literally the complete opposite, focused on the building aspect. They'd contradict each other.
I could see some simple stuff making it into TFC, but it'd be things like winches, water wheels and other simple motors for the purpose of functional design - gates, elevators, etc., but electricity? I don't think it'd fit.
Were I going to pack some mods together, the list right now would be MAtmos/Optifine for pretties, Redpower 2 Wiring, Logic and Machines; ComputerCraft, Balkon's Weapon Mod, Smart Moving, Double Doors, Fancy Fences, Useful Storage and Better Blocks & Items. Possibly Railcraft, I haven't played with it yet but it seems to add a lot of stuff that assumes you're using stuff like Buildcraft.