WordPress multisite with subdomain and directory simultaneously

It can be done, I’m actually using it for my private multisite installation.

  1. Install WP multisite and set it up in “subdirectory-mode”
  2. Install and setup the Domain Mapping plugin by WPMU
  3. Create a subdomain and point it to your installation. Add this subdomain via the Domain Mapping plugin.

By default your new sub-sites are accessible in a subdirectory but if you apply step 3 it can be accessed via the subdomain as well.