I have a little bit of a tough time rationalizing how a Leblanc could beat a Swain without ignite and how an Ezreal can have less cs than a roaming lane opponent other than you pointing out that it's silver. Those things I can't make much sense of.
AP Nasus, while never seen, is pretty viable though. He can still stack his Q and get a Lich Bane for it, but now his E and Ult will deal damage too. It's not as common since he get little use of his lifesteal and since he won't be as tanky to make use of his stacks as much, but the damage is higher assuming he still gets his stacks. It also makes up for his lack of lane presence and early game potential by having AP.