I think the Champions arc has great potential to tell a good story. Going to old maps for some instanced content will feel a bit reminiscent of the personal story and LWS1, and I don't think that's a bad thing. A reason to go back to an old map for new stories is fine by me. I just hope the length/quality of the story bits doesn't feel rushed or cut short. Hard to predict how it'll feel until we can play it, but I have faith they can have some good story content even if I've some trepidation to boot.
Edit: As of now, I imagine we'll get a new map for the finale. Maybe split between Ch. 7 and 8, or saved for the final chapter entirely. I suppose it's not impossible to do a big climactic battle in an instance of an older map, but it would be preferable to have a new, permanently explorable map, even if it's on the small side.