[hoppie]

Additional: I noticed that the tags field is being pre-filled when I look at the Add A New Topic form that sits below the list of posts tagged with tag X. That’s great.

What remains is the behaviour of bbPress when sending it a URL …/tags/X where X does not exist yet. The Forum now decides to revert to the default query and shows all available tags. It could, like a Wiki, have chosen to show an empty Topic list with the pre-filled Add A New Topic form. That would make sense to me.