Not viable, what? Veigar has always been viable and just not popular. As for Nasus, I contend that most people play him incorrectly. He's a fairly potent ap bruiser, post-6. People focus on his innate sustain and q, so they think ad bruiser, but building him with an unholy grail, lich bane (or frozen fist), randuin's, and abyssal makes him reasonably tanky and makes his spirit fire cause havoc on the battlefield, with your siphoning strike being a nuke. (His ultimate gives him free ad based on how much damage its dealing to surrounding enemies, so the ap REALLY synergizes with his kit more than people realize. Also, free max % damage is great against hp stackers, they give you more power. ) You could also build him all out ap carry if you really needed to, but he's a more effective bruiser. Start with q, but max his spirit fire first. It deals 50% of its damage up front, making it a decent poke, and it makes you impossible to dive because you will destroy the minions so fast when they get in tower range that they'll get caught by the tower before hitting you (plus your r, plus your wither, plus your sustain on q, rofl).