Possible to create a multisite network where the main site is non-WP?

I haven’t tested it, but it should be possible with these steps:

  1. Use example.net (not .com) as main installation for the multisite (or areallybigteam.com).
  2. Install WordPress with subdomains.
  3. Create the sites.
  4. Edit the URLs of all sites as you need: blog.example.com, team.example.com and areallybigteam.com.
  5. Make sure the document root for all these (sub)domains matches your WordPress installation root, except example.com which should go to another directory.
  6. Forget the subdirectory idea; this will not work. 🙂