For toplane Nasus, it's really not as big a buff as people are making it out to be.
Every third minion wave has a cannon, and a wave spawns every 30s, and he gets 6 more stacks for the cannon this patch than he did last patch.
This means he gets 4 more stacks per minute.
By the 15 minute mark, he'll have 60 more stacks than usual.
Is it good? Sure. Is it enough to let Nasus overcome the issues that kept him out of the meta? Not even close.
It's worth noting that now, Nasus is much stronger on red side than on blue, simply because he'll have access to Krugs. This was already true but the difference is even bigger now.