With 5.1.22 the support for Markdown is greatly improved and allows some Wikitext.
The problem with Wikipedia, is that it uses a lot of floating boxes and complicated CSS to get it's look. Getting that look into TW wouldn't be easy, no matter what approach you used. But grabbing the essence of a page isn't too hard.
Using the extension copycat, you can copy the markdown text of an article, and paste it into a markdown tiddler. It's fast, and editable, and communicates the main features of the original page. The styling with floating images and boxes, that's going to be different.
There seems to be a lot of denial in the TW community re the status of Wikitext vs. markdown. These conversations remind me (showing my age) of all those people who maintained that beta was better than VHS. It doesn't matter which is better, it matters which is supported and maintainable. Markdown has won, for better or worse. There is lots of support for it everywhere. TW is only supported inside of the TW project.