Heroic Blackrock Foundry will be available for x-realm raids when its released next week. But when is mythic highmaul going to be available for x-realm raids? Any specific date on 6.1 release?
Mythic Highmaul and Mythic BRF will, unless Blizzard changes their minds, be available for cross-realm when it is no longer current content. So both of them will be availible when the next raid after BRF is released.