Honestly I kinda wish Blizzard had gone through with their initial idea for Covenants where there would be a hard line on them only being available in the Shadowlands. You go back to Azeroth and the ability is gone, go to an Arena and the ability is gone.
What I think this would communicate is that the ability would not funcitonally change in the next expansion, it would just stop being relevant as we left the Shadowlands. As it stands Blizzard will probably go back to that decision for when 10.0 releases, but it's definitely going to feel less natural than it otherwise might have.