I expected to find this topic already opened… or perhaps my search was superficial? Anyway, how would the fellowship see the inclusion of all open files in the sidebar? At the moment, the sidebar only displays the outline of the active file. I happen to spread my stuff in separate small files instead of a single large one (one of several reasons for my switch away from OmniFocus and the like).
It is open to discussion whether tags would be listed in a unified sidebar list or in a separate list per file.
This might be the kind of feature that warrants a preference (i suspect some would be delighted to see it, others distracted by it).