Not sure how much of this is planned, but these are my suggestions for the flow editor:
Select multiple blocks and deactivate, duplicate, or delete: would be a checkbox system, and maybe a window select on desktop?
Convert a flow to a custom block: in the flow’s (kebab?) menu, have the option to convert the whole thing into a custom block. It would take any outputs from the trigger that were used and turn those into inputs. The user could then rename, reorder, or add more inputs/outputs.
Backpack: a great example of a backpack is actually on scratch. I haven’t used it in ages, but I think it’s just a small pullout menu that holds blocks or groups of blocks. Since blocks aren’t attached to each other, there could instead be a button to add them which would prompt you to select the blocks you want. When importing blocks, it would add them as a collapsed folder for easier arrangement. You could then click a button in the folder to “disband” it. It could archive stuff after a few days, or you could pin commonly used stuff to the backpack to keep it there indefinitely.
This is a lot so I obviously don’t expect you to add it all, just some ideas I came up with.