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?