Our guild has been chain running mythics since week 1.
Myself I have run 3 full mythic clears (3 110 chars) each week since week 1 (including the court of stars).
In our guild, 3 people have gotten legendaries (in this order: first a monk, then a druid, and then a DH).
1 week later, the monk gets his second legendary, then the druid gets his second, and then the DH gets his second (i.e. in the same EXACT order, and basically in a linear time frame between the drops).
So far, nobody else has gotten a legendary.
I know this is a small sample size, but the two other friends on my friendlist who have legendaries, have ALSO gotten 2. I do not know a single person who has 1. They either have 2 or 0.
I'm wondering if anyone else has any similar experiences, as it would be annoying if there was some kind of bug involved with the drop chance of legendaries.