Oooh. What if they did a "Tales of the Yawning Portal"/"Ghosts of Saltmarsh" style compilation of the old AD&D 2nd edition Ravenloft Grand Conjunction modules? (Feast of Goblyns, Ship of Horror, Touch of Death, Night of the Walking Dead, From the Shadows, Roots of Evil)
I would be so into this.Traveler's guide to the Shadowfell:
In this book we follow a caravan of Vistani (which is now a Background you can pick, just like it was a template in 4e; any race could be Vistani, since they welcome any lost traveler in the Mist willing to learn their customs) through the Shadowfell, where the demi-planes/prisons are located. We see Gloomwrought and the Palace of memories of the Raven Queen and a brief overview of the different prisons of the darklords and tables for the Dark Power effects in the region.
We also receive nice tables to make the dark-mirror version of your cities on the prime material plane, with Neverwinter/Evernight as an example.
The second book is X guide to Innistrad, where we pick off where we left our fellow Vistanis and now we use the mist to visit this MTG plane, with expanded sanity rules, corrupted monster template etc
Vistani's Guide to the Sigil & Planes
They could be the perfect hosts to explain the planes...
Who knows now that they're being re-envisioned?Do the Vistani do a lot of plane hoping? I thought they were mostly restricted to the Plane of Dread, but could travel between the different domains.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.