I’ve been working on a ‘three column’ version of Discourse for my own project for a little while. I’m not quite ready to share it with the world yet, but considering you’re working on something similar, I’ll let you know that I plan to release in plugin form in the nearish future.
The relevant part here is contextual ever-present columns. The columns are always there, including in topics (not in the admin panel though). All navigation is moved to a component in one of the columns. The components ‘know’ where they are at all times because I’ve added various route properties to the application controller that get refreshed each time there are any route changes.
This is slightly different from what you’re doing here, however it may have some cross-over.