My writers’ community has a separate forum area called “author threads” where anyone who so desires can start a single personal thread (thread title is their name, by custom) and post about anything they like, without worrying about being on-topic or off-topic or too personal or boring or anything else. Other people can also post in that thread, like any thread, but the eponymous author is its understood “owner.” We’re a very close-knit community, thanks in part to that forum area.
How about adding a category like this here? [0] Call it “User Threads” or “Journals” or …
Having one thread per user titled with the user’s name [1] makes the purpose of the category clear, so there’s less chance of contamination with other categories. (Pretty much every category in the BM forum has posts that belong in a different category, because the definition of what belongs there is left up to the user to interpret.)
[0] The “Life” category would seem to fit this purpose, but for whatever reason, it doesn’t seem to have much traction.
[1] Which can be anything, from IRL name to BM login to Master of the Universe Bow Before Me; as with any thread, the user picks it when they create it. But something other forum visitors can easily map to your Beeminder presence is probably advisable.