E max nasus ought to be addressed
Not because it's broken, but rather, it's incredibly frustrating to play against for many people.
In order to keep nasus mostly intact, here's what I would recommend.
Remove the massive nuke that occurs at the beginning of spirit fire. An undodgeable large AoE nuke is stupid in and of itself. Increase the base damage per tick for every level of E. This way nasus's E damage doesn't change at all but the damage is spread out through the duration of the E instead of having a big chunk of it being frontloaded to the very beginning.
Anyone who wants to E max nasus will still be able to push the wave hard, but will no longer be able to do everything safely, especially poking an enemy out with little to no counterplay.
That being said, something needs to be done to either slow down the pace of the game so that Q max nasus doesn't feel shitty or so that nasus gets more of an incentive to invest in his Q early (essentially, buff the Q somehow).
EDIT
Guys, this isn't about AP nasus, this is about what some know as "Quasus" which is E max first into traditional build nasus (tri force + tank). The reason why I refused to call it quasus is because he was far from the first to ever max E first in lane, and therefore, I don't believe he deserves any credit for anything other than just popularizing what already was.

says hi
says hi
and takes Thunderlord's. As he can proc all 3 stacks quickly.