I'm not sure that article attention is necessarily always going to be the limiting factor, otherwise you'd expect there to be piles and piles of fancruft all over Wikipedia, meticulously maintained by obsessive fans.
One argument for not being just a universal repository for any kind of information is that it may make it much harder to navigate to actual information you care about, where encyclopedias are supposed to generally be a digest of the information available about a subject. There's also the issue of proper namespacing for this sort of thing, since if you let there be an article on every single person and every single piece of information, you can imagine that there would be a large number of name collisions, making navigation a bit tricky (The disambiguation page for common names would be insanely long, for one thing).
I think the proper way to build a "repository of all knowledge" on top of Wikipedia would be to spin off daughter Wikis (e.g. wikitionary), where in-depth curated information can exist that break out content from Wiki articles (for example, Wiki has an article about a given album, but WikiMusic has an in-depth article on each song, with curated links to reviews and articles about it, etc). I think we're seeing some of that already with the various sister projects to Wikipedia.
If you really want a “repository of all knowledge”, though, the main thing you need is standardization of wiki APIs and dump formats, such that you could, say, create DB dump file that contained “Wikipedia, all its siblings, and every Wikia wiki” and fixed up all the links between them.
One argument for not being just a universal repository for any kind of information is that it may make it much harder to navigate to actual information you care about, where encyclopedias are supposed to generally be a digest of the information available about a subject. There's also the issue of proper namespacing for this sort of thing, since if you let there be an article on every single person and every single piece of information, you can imagine that there would be a large number of name collisions, making navigation a bit tricky (The disambiguation page for common names would be insanely long, for one thing).
I think the proper way to build a "repository of all knowledge" on top of Wikipedia would be to spin off daughter Wikis (e.g. wikitionary), where in-depth curated information can exist that break out content from Wiki articles (for example, Wiki has an article about a given album, but WikiMusic has an in-depth article on each song, with curated links to reviews and articles about it, etc). I think we're seeing some of that already with the various sister projects to Wikipedia.