I'm not sure if it's easy to re-categorize posts a-posteriori, but if so I would naturally go @dbuenzli's route, creating categories as we see that becomes useful. Note that the Rust Discourse has very few actual categories (
meta), maybe the Discourse interface does not make it as useful as for a traditional forum.
Among their categories,
help corresponds with
beginners (both names are fine), and I think
announcements is a reasonable idea as well (that is a regular source of content for the caml-list, although one can also wait to see if people want to cross-post them here as well), and
meta may be relevant anywhere.
I don't expect ICFP to generate enough discussions to warrant a category, but feel free to open a topic to discuss it (and co-located events)!