It's a lovely theory, but put into practice it's a lot of work to maintain, especially with more than one editor. I was a proponent of this concept for a long time, but it's just not worth it [1]. If you want to be able to align the leading edge to something other than a tab stop you are better off from a practical perspective to just enforce the use of spaces.

[1] Think in particular of when code moves around. Sometimes it moves to a place where the indent level is different but the total number of expanded spaces is the same. This looks fine until you look in another editor.