This process is overly complex. I also think GitHub issues and Trello would be far more convinent for an open source project (as the UI is much easier to use and is familiar to more people).
The main problem with using a kanban (trello like stuff) backed by GitHub is that it’s not meant to be used that way. The idea of a kanban is to track who’s doing what, and where they are. It’s meant to be very visual, where far left hasn’t been worked on, and far right is done, with progression in the middle. Issues trackers however, should be used to manage information about issues. When you combine the two you end up with a huge mess of 700 tickets on a kanban board.
tl;dr Use trello/kanban for tracking short term progress; use issue tracker for tracking the actual issues, not the progress of fixing them.
Of course things like, “working on it soon”, are fine in your issue tracker, how else do you tell people you’re going to fix it?
I played around a bit with Waffle, and it looks like you can configure it to require a special label in order to show up on the Waffle board in order to reduce clutter.