Ok, yeah, I just kinda made up that word.
I've been trying out the Arcane-less Marksman build and... I don't know if it's had a noticeable effect or not.
My current Armor Penetration (I've been told I shouldn't use that word in raid chat) is a little lower than I should really have to do it - I think I'm down to 475, with the Scorpion for procs, but I was over 500 when I respeced. But getting 2-piece T10 and going from the T8.5 to the T9 breastplate otherwise made a lot of sense.
Anyway, as much as I love that Marksman is about having lots of shots, I think dropping Arcane makes for a more logcial rotation - and, except for when you have to push extra buttons for Rapid Fire, Readiness, and such, it really is a rotation again: Chimera, Aimed, Steady x4. Kill Shot mucks it up a little, but critting for 20k is awesome (thank you, Void Boss Dude in Violet Hold, and I hate you, combat log bug that prevented me from screenshotting said crit).
Really, with my current level of ArP and the Scorpion, I should be doing a Chimera/Aimed/Arcane/Steady x3 type of thing, and only dropping Arcane during procs, but given the unpredictability of procs, it's really not practical. I'm not that good.
My DPS is definitely up a bit - I broke 8k on I think one of the spiders before Lady Deathwhisper the recently in 25s, and I broke 6k on Festergut in 10s (the night we don't have a log for, damn it, but I did at least screenshot that) - but that's just as likely due to gear changes as the spec/rotation change.
Dropping Improved Arcane from my talents was a bit sad for me; I absolutely loved the talent when it was a reduction in Arcane's cooldown. Ten-second and five-second cooldowns would have been mathematically easier to plan for... if our GCD weren't stuck at 1.5 seconds. Anywho, dropping Improved Arcane let me pick up Improved Steady, and since my rotation is stacked the way it is, the buff from Improved Steady is always going to Chimera.
One nice benefit of not regularly weaving in Arcane is that when I need an instant shot now - say, for web wraps or some such - I have one conveniently off cooldown to use. And I can still toss it in when I have to move.
As my gear gets upgraded (please, please let the cloak and belt be next), my ArP should go up, and it will be a more solid switch, but for now it's at least not hurting.