It's been a long, long time since Nasus has seen any competitive play. Back in the dark days of preseason 1, he was actually viewed as one of the most important champions in the game, simply because he could survive a 2v1 lane quite easily and thus enable your team to take a jungler -- something that was far from a given way back then. His E, Spirit Fire, was and is one of the most potent waveclear spells that any melee champion has access to, and it easily wipes out minion waves in no time at all during the entire game.
The last few years haven't been kind to Nasus, however. Despite his rework back in 2015 that totally broken him in solo queue, the champion has remained unpicked in competitive play for pretty much the entire history of the LCS. Why? Simple mobility creep. It's extremely difficult for a Nasus to get into range to hit anything at all of relevance, meaning that a 1000 stacked Nasus can easily get killed in teamfights without doing anything, as he is a slow melee champion with no real gap closer. Even giving him extra range on all of his abilities while his ultimate was active couldn't change that.
However, Roccat seems to think that an entirely different build from the standard might be the way to go. Betsy, the mid laner from Roccat, locked in Nasus in order to take on Perkz' Syndra during Roccat's first game against G2 Esports and built into a very unorthodox ability power build. Instead of looking to leverage the power of Siphoning Strike like a traditional Nasus build, Betsy instead looked to annoy enemies to death by investing fully into Sprit Fire. He maintained the same split-push power that a traditional Nasus build would have brought to bear, but brought dramatically more teamfight utility, as it's difficult to ignore Liandry's empowered Spirit Fires.
While Roccat did end up eventually losing the game, it wasn't wholly the fault of Betsy. AP Nasus looked both annoying and surprisingly viable. Considering it's also completely impossible to interact with in lane, I would expect to see AP Nasus soon in a solo queue game near you. How well that will go...Well that's another question.