The new Slayer Tree is growing on me (besides the reduced Cooldown on Overpower. As is that node would be completly irrelevant.) the more i read it however it stings to read Slayers Dominance. Reason being that Fatality should already work similiar to the way Slayers Dominance does.
Cleave is included as an Ability that applies Fatal Marks however having tried this its just way to hectic in Aoe Situations to identify the Targets with Marks and execute them before they die in a Pack with different ammouts of Targets at different health. The Reward for pulling this off is also really low.
Slayers Dominance (or rather the whole Tree) is succesful in making Execute more usable in both Aoe and Single Target Situations where Fatal Mark fails.
An Idea to make Fatality more relevant in Aoe Situations would be to cause the Fatal Mark to explode if not consumed after the Target dies. Another way would be to just copy the last Paragraph of Reapers Mark on the Death Knight Deathbringer Tree and just staple it on there. The Ammount of Stacks that can Travel could be limited to stop any sort of exploits.
Fatality (or any Capstone in my oppinion) should not be completly irrelevant in Aoe Situations. Not to say it should be on par with Bladestorm in Aoe but right now its not even usable. The Paladin Tree pulls this of very well. Execution Sentence is not so good in Aoe but still usable on priority Targets while cleaving. Final Reckoning is not so good in Single Target but still very usable in pure single Target. Even Divine Arbiter does some cleave Damage. I think Fatality should also be capable of being useful in Aoe.
I know some people dont like Fatality for how boring it is but i think the Idea of it is good enough to expand on it. Move it one row up and add Capstones to it that would push how useful it in is in ST or AOE.