I am not sure they need a starter set given how much material is already out there for free, especially since I can't imagine they could ask much less than the core set for a good starter set.
Trimmed down rule book? Dropping that away from a hardcover might work.
There’s space for the Sablewood to become an actual set of Situations with a bunch of prompts for the GM to ask player input in how the narrative flows. A good level 1-3 flow or something, with ideas where you could go next outside of that.