a great feature finally landed in Discourse: wiki posts. Through a new flag, admins can switch on collaborative editing rights for all logged in users on posts, allowing anyone to contribute and keep the post up to date. You can identify those by the edit-glyph right under the posters picture:
I've set this flag to both the discussion on How to get notified about topics as well as the topic about How to find great pictures under creative commons, allowing any logged in user to edit and extend – please feel free to do so.
If you have any other topic, you'd like this feature to be activated on, please let me or anyone else of
@admins know and we'll switch it on. My idea would also be to migrate the Handbooks here, too and make them collaboratively editable.