That's great, thanks! For now I have
forked the koreader repo and am working off that. Screenshot of the work so far is attached.
It's currently implemented as a plugin, but I plan to either strip out or at least hide the main KOReader UI… my goal is something simple that ex-Pocket users will feel at home in and is as close to a "native" Kobo app as possible. We shall see if building on KOReader is the right approach… rmkit looks promising too!