I think the general concept of Marksmanship is fine, but a few key tweaks would take it from good to great for sure.
1. Petless would be wonderful. As it is, there is zero interaction with your pet already (though the same can be said for Survival) unless you take Lynx Rush, which is 1 button every 90 seconds.
2. I whole-heartedly agree with the need to make Careful Aim a cooldown rather than percent-based. Hell, as far as I'm concerned, fuck Rapid Fire and make it a cooldown that does what Careful Aim does. Rapid Fire can go straight to the toilet.
3. Steady Focus is tedious and just flat-out irrational. You can run around while casting "Steady" Shot, which makes it not very steady at all. Doing that twice in a row somehow means you shoot faster for 20 seconds? Stupid from both a gameplay and logic standpoint. I'd rather have Steady Shot be renamed to something more logical and have it give us a 10-second buff that actually matters, that way we aren't forced to shoot two in a row (which can be a pain in the ass with Thrill of the Hunt procs - hello capped Focus).
4. I kind of miss some of the creativity that they took away from Chimera Shot. It used to be able to disarm, drain mana, etc based on what sting you had up. We don't have to re-introduce all of those stings, but it would be cool to get some of the neat utility options back into it. Right now it's, wait for it... An instant shot that hits really hard! Meh, boring...