Armstrong has posted up a speculative article comparing Executioner enchant to Mongoose enchant. As it stands, typically Mongoose is the defacto tanking enchant. That may all change with the addition of the Executioner enchant.
Assuming a similar proc rate as Mongoose, Executioner will out threat Mongoose on all but the most heavily armored bosses. We’ll see how it pans out when patch 2.3 comes out!
EDIT: I had incorrectly put that this enchant would come out in patch 2.2, but it is to come out in patch 2.