For the first time this expansion multiple things are happening for our class and players as a whole making playing multiple specs somewhat a good idea
1: Both specs are going in quite strong without any spec having a huge lead in single target or Aoe
2: having both specs with concordance is relativly easy if you have ak40
3: both specs share similare stat weight and share quite a lot of bis gear. Only issue here will be fury needing to go with the tier hands while arms don't.
So going in tomb switching specs seems like a good idea if some boss design favors one spec while some the other.
Here is my plan going in, without any prior testing, so feel free to disagree and share toughts.
Goroth: Arms
Demonic inquisition: Arms
Harjatan: Fury
Sisters of the moon: Arms
Mistrss Sassz'in: Fury
Desolate Host: Fury
Maiden of vigilance: Arms
Fallen Avatar: Arms
Kill'jaeden: Arms