There are really 2 parts to this: finding posts that already exist, and encouraging new posts in different topics. Micro.blog is still small, so the most value comes from solving both of those together.
Livejournal is the example that I thought of (and have experience with). Everyone who joins LJ automatically gets a personal blog which functions as their identity account. Furthermore, you can also create community blogs about any topic, but you need to have that requisite personal/identity blog to do that. Anyone can either “watch” a community blog without prerequisites, or fully join to get posting privileges. Your posts to the community blog reside there, but are identified by your LJ identity; your personal blog is separate to this.
I can see something analogous working on Micro.blog. Everyone already has a personal blog/domain. Perhaps there can be a way of creating the M.B equivalent of LJ’s “community blog” — a particular topic specified by user(s), which other bloggers can then “post” under. The blogger still owns their post on their blog, but M.B can congregate them based on these user-specified topics.
This is along the lines of @Cheri‘s suggestion of “tagmoji ambassador”. Yes, user-specified, user-owned, public, unmoderated tagging and community-building starts moving in Twitter’s direction, but perhaps this can be steered more towards Livejournal (private, moderated)?
** Bolded words were edited in later.
While tagmoji works well for general/functional categories, I’m of the opinion that they’re incapable of communicating the kinds of specificity that users desire; I already find Cheri’s examples of “writing”, “programming”, etc, too general to be of sustained benefit; one has to resort to a text search to supplement tagmoji’s limitations. That, and the inability to customize text-tags and/or tagmoji, already limits identification and retrieval of specific posts on M.B (and thus, finding like-minded users on M.B), as @bradenslen pointed out.
I suppose the next question is whether this kind of Livejournal-esque method of aggregating topical interests suits the vision and direction of Micro.blog.