> Ok, I see what you're saying. You're proposing to have TODO states and
> other tags on the left of the heading title in fixed pitch, and the
> heading title in variable pitch. In my current setup the whole heading
> is fixed in Agenda and variable in normal buffers. I agree it would be
> good to have mixed-pitch headings.
>

This is doable for the TODO states already using the org-todo-keyword-faces
variable, which can contain full font attribute lists, like this:

    (org-todo-keyword-faces
     '(("TODO"         . (:foreground "DarkOrchid1" :inherit fixed-pitch))
       ("INBOX"        . "cyan"))

--Diego