Another possibility is:
/castsequence Arcane Shot, Chimera Shot, Aimed ShotLogically it would run through the cast sequence first on every click; I'll have to see if it will actually go to the /cast line when those three are unavailable. (The downside of doing all this on lunch at work.)
/cast Steady Shot
I think the cast sequence would still choke, though, in terms of the 6 second/10 second optimization; the first two iterations would be fine :
Arcane shot, Chimera Shot, Aimed Shot, (1-2 Steady Shots depending on haste), Arcane will be ready so Arcane, Steady, Chimera, Aimed, Steady, Arcane, Steady, Steady, Chimera, (Arcane would go here except the cast sequence goes to Aimed) Aimed...So the cast sequence will still eat a couple Arcanes. I'm actually not sure purely manual weaving would help, since there may still be times that Arcane is ready at the same time as one of the others.
It might, however, help the macro be more flexible for variable haste with regards to Steady Shot - since the hunter GCD is static at 1.5 seconds, and Steady Shot's cast can't be made faster than that, if you're not stacking haste to keep it constantly at a 1.5 second cast (and my gear isn't good enough to even try doing that yet), it's Rapid Fire and Imp. Hawk occasionally boosting your Steady Shot cast speed (plus Bloodlust, and I'm liking Potions of Speed recently - need to fish more for more pygmies). The current macro doesn't effectively take advantage of that in terms of the occasional extra Steady Shots, but if the /castsequence + /cast macro does, it might be worth switching to.
I'll try it out on the dummies when I get home if I can fish up enough pygmies to make enough potions to test out the haste effects.