I toodled around in the new Tekkit a little. The biggest change is that IC2 is gone. I notoriously start out the game with IC2 machines, so it took a little adaptation. BuildCraft is still in game, so quarries are still making 64x64 holes in the ground.
Now the heavy lifters are Thermal Expansion and MineFactory Reloaded. Logistics pipes are also gone, replaced by the superior Applied Energistics inventory system.
Good changes, except the loss of RedPower2 :(