I presume the point is not what was already built but what was possible: Wikis have existed for a very long time, and nothing about Wikipedia seems difficult to do with very old versions of Netscape.
Also, email and IRC were available before HTTP/HTML, so people were definitely able to communicate over the Internet, in realtime or otherwise, even before they were viewing Web pages.
Indeed all those sites mentioned are just manifestations of an idea that is really independent of any "progress in web standards", and had someone thought of the idea 20 years ago, they could've just as easily (or maybe even more easily - because of the relative lack of complexity back then) set up a site for it.
