If you define wiki-style format as a functional goal such as a service that allows collaborative editing of its content and structure by its users, then all of the options you listed allow this. Communities + Knowledge is perhaps the closest in terms of what you want. It allows collaborative edits and it has a lot of content management machinery that underlies a wiki. And, sure, yes, you can write custom code to make it more, ahem, wiki-like.
Reading between the lines of your question, it seems that you and perhaps other folks on your team have a preconceived notion of how a wiki should look and feel versus what a wiki should do. Could you get there with Salesforce? Perhaps..but that would be reinventing the wheel. There are a ton of OSS and commercial wiki solutions. One obvious example is StackOverflow for Teams.
To build an internal wiki on Salesforce, you could simply create a tab/button/link that launches a non-SF wiki app from SF with, say, SSO and call it a day.
If you describe wiki-style format as a functional goal as a service that allows collaborative editing of its objects and structure by its users, then all of the choices you listed allow this. Communities and Knowledge are the closest in terms of what you want. It will enable collaborative edits, and it has numerous content management machinery that underlies a wiki. And yes, you can write custom code to make it more wiki-like in Salesforce chatter Wikipedia.
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