If you regularly hit and stay at 100 focus then you're rotation is wrong in some way, right?
My answer is: yes, but I end up doing it now as a marksman hunter.
And I do it much more often now thanks to having the Burning Adrenaline buff active (from 4pc T12). This can have you completely swimming in focus. And it has a bug that makes that swim in a lake instead of a pool.
Here's the issue. Some shots only register when they land on the target. The Burning Adrenaline buff is only removed when the shot lands. If you are far away from the target there is a travel time to the target. Say you're a MM hunter. You have the buff and have 100 focus, fire a "hardcast" Aimed Shot and then immediately a Chimera Shot. The buff will be consumed and both shots will be free.
This in theory is a boon, but really it just screws up all sense of rhythm for the MM hunter. MM hunters always want to do two steady shots in a row to keep their +15% haste buff rolling. Letting that drop is a bad thing. They also have a fairly close call on their Chimera Shot. Letting the sting fall off is a bad thing. And they're good hunters who have trained themselves that capping focus is bad which is exactly what will happen after allowing Burning Adrenaline to consume an Aimed Shot.
So what is there to reach for for a MM hunter? Firing two or three Arcane Shots takes a lot of time and will let something in your rotation fall. Hitting Kill Command eats a big chunk in one shot for a little DPS ... and it might not actually work if your pet isn't meleeing.
I think the right approach is to try and lob in as many Arcane Shots as possible and try to at least start the first SS while your ISS buff is still active. This may cap your focus a bit too long. KC may be better. But choosing Arcanes will set MM up nicely for the T13 bonus and it works for our BM and SV specs too. Of course BM or SV should prefer to use KC and ES as always, but sprinkling in Arcanes is good for them too.