Add ability to follow individual accounts
It is possible to post unlisted, which (for our purposes) means that statuses are publicly accessible but not published in the public hashtag feed. Because these statuses are publicly accessible, we ought to be able to retrieve those statuses without authentication.
This would probably mean a fourth URL template and/or perhaps a separate method of entering individual accounts. (It is customary to add accounts as
@user@domain, which means that there's no reason to scope account addition to a host-based dialog.)