I believe they said it would only be applied for dungeons in Shadowbringers specifically for right now.

So it'll help you out if you're starting fresh as a 70 going forward, but if you want to experience the rest of the game prior I don't think they have it in the wings yet. Nor do I think they could for events in HW unless they're going to let you take someone like Pippin or Arenvaldt(from whatever the hell they're doing) for tanking if you're not able to.