As one of the posters in a linked topic it is noted that there are three things useful for creating wiki topics on Discourse.
One which you noted (What is a Wiki Post?) details converting a regular post to a wiki post meaning that any user with the correct trust level can edit it.
Another which you noted (DiscoTOC - automatic table of contents - theme) adds a table of contents to only the first post of a topic.
The third you did not note specifically but mentioned is Knowledge Explorer Plugin which you may or may not have the ability to install based on your service plan or self-hosting.
For many months our site has had Wiki pages in a separate category with discussion pages in a related category. The Wiki pages are kept to just one post and the corresponding discussion pages work as normal topics.
Yesterday having learned of the (DiscoTOC - automatic table of contents - theme) added it to a few pages and allowed those with trust level 3 and higher to start using it.
In the other post (Is anyone working on a Discourse Wiki?) an example of the table of contents was given with Knowledge Explorer. I didn’t know it at the time but that page makes use of two of the noted items, DiscoTOC - automatic table of contents (theme) and Knowledge Explorer Plugin. Since our site is not on a service plan that allows the Knowledge Explorer Plugin I can’t elaborate more on it.
A single post seems pretty different than a full wikipedia-like page, so I want to be sure it can work and be stable.
It works on our site and is stable. As I noted the discussions are moved off to a corresponding post and since I have admin rights on the site, I can move any replies to the discussion post. I did try some things to limit replies but was not happy with the outcome; open for suggestions.
The main reason it is stable is because most users on our site don’t contribute to the wiki pages. I also see the same thing at StackOverflow where many would rather leave a comment about a needed edit rather than just making the edit. Also its good to know that all post on Discourse have an edit history and can be rolled back.
One other thing about wiki pages that I view much differently than many is that they do not have to start out cleanly. One of our most popular and most commented on topics is at present and has been for many months, just a growing collection of links, excerpts, comments, etc. The idea is that as things are discovered related to the topic (Bug hunting toolbox) it is just dropped into the wiki post so it is not forgotten.
It has reached quite a sizable list and now needs to be reformatted and filled in with more details and working examples. The table of contents theme gives us the ability to take the next step and organize the information with an ease of finding something faster than reading the entire post.