SO will never be wikipedia and that is OK.

What we miss the the middle ground. And that is open for the taking! (hint)

SO is transient and disposable. It is about the error message of the day and by chance hits the language/pattern of the year. Wikipedia is about stablished knowledge already accepted and published. The open spot in the middle is about accepted techniques for the pattern of the recent years. Those are filled currently by random blogs, posts and news aggregators.

It's debatable whether they achieved it, but at one time Stack Overflow explicitly stated that their goal was to be a middle ground between a transient Q&A site and a wiki. That philosophy is why they allow everyone (even those without an account) to edit posts and why they close duplicate questions.

They can say whatever they want. But they are not and never will be.

Their community management tools are awful and the philosophy they and the moderators abide to is that questions/answers must be closed as soon as possible.

For example: take one question such as "how to do X in Y". The answer today is "not possible". it is accepted. done. Tomorrow it is "now you use Y.abc" and that old question will never be updated because the person who asked is not interested anymore, or worse, it might even be locked. This is a very common pattern. There's also thousands of the "A: copy and past this, which i do not understand either" which completely kills any knowledgeable discussion.

Arguably, SO is already a Wikipedia for techie matters. It's just very poorly maintained and quirky.

Just like regular Wikipedia.

Wikipedia is usually much more presentable, in my experience.

Depends on the topic. Stuff like political topics are a mess.

How would that work? A site to collect common code snippets?

As if Wikipedia never shoves banners in your face. I'd rather have the stackoverflow model than the Wikipedia one. As for collaborative, try the edit button on any question or answer. It's already a wiki. If you have enough karma, you can put your words in anyone's mouth; if not, it gets into a review queue. I'm one of the people with enough karma to process that queue, there is very very little abuse actually. You can even submit anonymously, on Wikipedia your IP is then published but on SO I just see "anonymous user". Again, stackoverflow already has the better model. Finally I'd like to add one point to the two comparison points you already mentioned: the Wikipedia syntax is one of a kind, weird and you need to learn it specifically for Wikipedia (and other MediaWikis, but they're not that common that everyone already knows it). Stackoverflow just uses markdown, which as a developer is not something you won't already partially know. Let's not turn it into Wikipedia.

So like the ArchWiki but for all things tech, not just Linux?