to clarify, if you could figure this out, i would gladly pay you (within reason!) to figure it out and document the app and integration for the larger ghost community - it sounds like many people could use a commenting-rights role (on drafts as well as published, but drafts are much more important), and without granting full editorial permissions (!)
There’s not a good way to hack the ghost admin side that doesn’t involve changes to core, although it’s possible to write one’s own code and run it separately, via access to the api. (This is the approach I took on Phantom Admin.)
And then it’d just be a question of going to marker.io to look at the feedback, or else telling marker.io what issue tracker you want your feedback sent to.
btw, my apologies: this is a very clever workflow hack, and then simply hide the tier from signups and add editorial assistants as complementary subscriptions! main idea behind marker is the location-specific commenting ability around long-form content. it also allows for workflow tweaks and adoption of an editorial process, replete with triaging for actual editors with rights, etc