Digging into the project I reckon Apple will abandon macOS by the time Darling is able to run a graphical Cocoa app. It’s an interesting project but Cocoa != Win32. There’s an awful lot of APIs (including AppKit, which they haven’t started yet) they will have to rewrite. That’s an enormous among of work for 4 developers.
The Windows version of Scrivener runs well under wine and if Keith and Lee make good on their claims, version 3 will have feature parity. Use that instead.