There are a lot of good mods that tekkit needs to be great because most of the ones it has are confusing at best and are hard to use, so I think we should add:
The Aether
Clay Soldiers
Elemental Arrows
Smart Moving
Mob Dismemberment
Millenaire
And maybe the Gun Mod if Sphax makes a patch for it
So thats what I think should be considered to be added into tekkit if the are compatable