Just read the Dark Heart backer supplement. Thoughts:
The Planescape love is on full display here, and it feels great! I’d been knocking around the idea of running a Planescape-inspired DW game before I ever heard of this, and now I’m not sure whether I’d use the original Planescape boxed sets or this.
“Populating the City: Rules for the intermingling of species” gives me a curious sort of warm fuzzy. Great way to acknowledge sexuality and introduce it to a DW game that (a) is notably different from the AW/Monsterhearts sex moves, and (b) feels perfect for the setting being described.
I’m not as sold on the mechanical stuff as I am on the setting. The author appears to have abandoned several DW move principles for no discernible benefit. You’ll find moves where the GM rolls (not just table lookups, of which there are many), and moves that explicitly ask you to retroactively fit the fictional situation to the dice roll, both of which feel very DW-backward. I’m curious what the design impetus is behind these things.