First of all Let's try to keep these two concepts separate shall we?
Mythic = A new End-Game difficulty for Lvl 30+ Characters similar to the old Epic difficulty pre MotU!
You have to be capable of running EE MoD without dying before even attempting to run these!
Killer DM = A new Uber difficulty for EVERY Quest in the game - Above and Beyond Elite!
Triple Completionists who find it boring running Elite Storehouse's secret can now try it on Killer DM mode where the Puzzle acts like the one in Delirium and 50 Sahaugin Champions are constantly attacking you while you attempt to solve it!
Now - The difficulty I want to see is Mythic so that Epic Levelling can go back to being you know LEVELLING!
And I've always been against a so-called Killer DM difficulty for reasons I've stated on numerous occasions.
BUT If these suggestions are going to keep being bandied about let's please get our terminology down so that we can keep the suggestions to one or t'other rather than getting mixed up about what the OP's actually asking for!