Mythic gear will be very close to conquest in wpvp, and will be between honor and conquest in instanced pvp. Weapons and armor will be no issue since the formula is exactly the same as pvp gear, but I see problems with trinkets with different procs. We don't know the options for trinkets but there is a huge chance for disaster.
Blizzard should make sure that no one is forced to run mythic raids to get bis trinket for pvp (especially in wpvp where mythic is even stronger).