I like the idea of having all of those within the actual VCS, mostly because with Git you need centralized services like GitHub to provide that.
But I have to ask: Is it really a good idea? Seems like feature creep motivated by the wants of a single project (SQLite).
All of those could be (albeit awkwardly) backed with a git repo and a cron job. Wiki? Just make a repo with a bunch of Markdown or this-week's-favorate-markup-language files. Ticketing & bug tracking? Again, just a Markdown file for every ticket. Embedded documentation & technical notes? Those are just special wiki pages with different attributes. Forum and chat service? Do you want your VCS to do that? I get being able to hyperlink between files and conversations, but still.