The way I use KanBan currently in my vault, is that I got lanes related to areas of interest, and if it’s a smaller task it’s just got a task within the main KanBan note.
If however the task is part of a larger project (that is 5-10 subtasks), I create a note, and have that note linked from the KanBan board. This gives an overall status of the task in the board, and the details can be viewed/edited through the popover view.
At first I considered it a drawback that the KanBan task (with the link to the project note) wasn’t updating accordingly to the project tasks, but when thinking it over it’s actually kind of advantage, as you can then keep them separate, and move the KanBan task of the project around independently of the project tasks, if that make sense.
I’ve also had tasks spread across the entire vault, and found it disheartening and slightly confusing, so restricting myself to either the KanBan board tasks or project notes with task is kind of liberating and gives me a better order of my complete set of tasks. But your mileage may vary.
Another point related to your original request, is that actually gathering all tasks from all over the place, and still allow for some drag and drop functionality where you need to keep track of origin of tasks, and what tags/query parameters caused it to end in a given group, is actually a rather hard task.
The plugin CardBoard aims to do this within a KanBan style board, but I don’t think they’ve figured out the drag-and-drop yet. And now it hasn’t been updated in a year either.
Another similar project is the Task List Kanban, last updated 5 months ago, and now in a state of no longer being maintained. I’ve not tried it, but it claims that it do use drag-and-drop based on a tag (equalling the column/lane name). It can collect tasks either from the current folder, or all over your vault.