Nasus needs buffs, but maybe the R change is a little overkill

Just changing E from 40 flat pen to 35% at max rank was probably enough. Between either zhonyas, tabi, or GA, most squishies end up with a wee bit over 100 armor late game, and so 35% will keep him just as good against squishies while making him WAAAAYYYYY better against tanks and bruisers.

Adding 50% base cd reduction on Q in ult is probably crazy.

I'd rather he just have all the resistances frontloaded on ult activation, which is still a good buff, but not as crazy as the Q change during ult currently planned.

If that still isn't enough, you could probably try for some sort of interaction between wither and spirit fire. Something like, while enemy is in spirit fire, wither's AS cripple is made 5/10/15/20/25% more effective based on wither's level (wither never maxed first, so lane phase should still be very weak. Also, it's made more effective, not adding %, so max level wither inside spirit fire would be 50% times 1.25 = 62.5% cripple conversion, not 75% cripple conversion), goes away immediately upon leaving spirit fire AoE.

Just some thoughts because I don't want nasus to be overbuffed, and I think current plans for him are an overbuff

TL;DR the spirit fire change is a gigantic buff, so everything on top of it should be tame, and the current Q during ult change is another gigantic buff instead of something small.