Posting it again here, due to comment system fail.

The difference between a haste-stacked Aimed shot focus dump or an Arcane shot focus dump is not as large as most people make it out to be. Yes, Aimed focus dump is theoretically higher damage, but if you have to even interrupt one of those AiS casts to move, it can potentially be a damage loss over arcane.

You're probably aware of that already, but based on how movement heavy fights in Dragon Soul will be, it's may be better to stick with Arcane as a focus dump. This of course is all speculation. We shall see.

Further, I have qualms with the 2p bonus as a Marks main. With the change, it will mean that we will be steady shotting less in MM, which makes it harder to keep up the improved SS buff, which is already quite unforgiving to prevent from falling off (miss even one SS in your rotation and the buff is likely to fall off, = substantial dps loss). Unless they increase the duration of ISS, I have mixed feelings about the 2p bonus as Marks.

When you think about it. We use about 4 stead shots to fill up on focus and 2 is enough for chimera or aimed shot. So, it is creates more focus (Depending on how much) It will take us 2-3 to fill up and we will have more focus to dump with Arcane/aimed/chimera shot. I think its a plus

With the mechanics of the 2pc and 4pc bonus for Hunters, my initial impression would seem that a MM rotation would be fitted around the ISS uptime (yes, we may get 25% haste from AS on 4pc, but why sniff at another 15%?)

So the priority will read:

SSx2 for ISS
CS on cooldown
AS filler

So it'd be like SS - SS - CS - AS - AS - AS - AS - SS - SS - AS - CS - etc.

Basically, goodbye somewhat standardised rotation, hello chaos.

Of course, I could be well wrong, I'll wait and see what happens when more skilled Hunters test the set bonuses on the PTR say.