Starting next week, cross-realm groups can enter Mythic difficulty Vault of the Incarnates!
(Source)
With the weekly reset in each region the week of February 14, we will enable cross-realm groups in Mythic difficulty Vault of the Incarnates.
This represents a shift in philosophy that has evolved over the last few raid tiers, where we’ve seen the pace at which the Hall of Fame filled up for both factions become unaligned with the timing that we would have chosen for players at large.
We will still maintain a Hall of Fame for this and future raids. To qualify for it in cross-realm groups, you must simply have at least 16 players from the same guild taking part in the raid.
With future raids, we’re looking into a more-scheduled approach for when cross-realm Mythic difficulty becomes available. We want to keep our options open for the timing to vary, since we yet don’t know the circumstances we might observe in the future, but we intend to provide further announcements like this one to give players time to reorganize.