The problem I see with federated wikis is potential creation of echo chambers. Current Wikipedia is often a political tug-of-war between different ideological crowds. For instance, on Russian Wikipedia, Russian Civil War article is an infamous point of struggle between communist and monarchist sympathizers, who often have to settle at something resembling a compromise.

If both sides had their own wikis, each would have very biased interpretation of events. A person who identifies as either communist or monarchist would visit only the corresponding wiki, only seeing narrative that fits into their current world view, never being exposed to opposing opinions.

I think many people in the comments suffer from some version of curse of knowledge.

Sure, this feature us quite irrelevant for a power user who is quick to navigate the browser and needs a split second to remember what tab it is simply by reading the header and seeing the icon.

However, many less proficient people can benefit from this feature. Not once I saw how someone who has 10 tabs open and needs to go to a different webpage, starts meticulously clicking through every single one of them because they have no idea how the page they are looking for is called, they are too overwhelmed by using web as a whole to take notice.