Cyrious mentioned this in one of his recent videos. I ask for this change because you have very little time to react to these guys coming. It'd be nice if they needed to fill up. That way, you can target landing pads and have some time to take out the Liberator, which would need to land to take troops, and actually deal with these guys. It would also force them to have to come back to a pad if their spawn beacon goes down and their men die, instead of having them hover in the area and keep spawning people.
You need logistics specialist to spawn in a lib. Besides, most just pull libs from the warpgate anyway. You probably meant valkyries.