No, this is not currently possible with GitExtensions
You might want to use TortoiseGit for that kind of integration with the Windows Explorer.
Question
I'm wondering if I can/how can I configure git extensions to, when I explore a file system with windows explorer, show me which directories/files have git repositories in them, and, of those which have repositories, which have been touched.
Solution
No, this is not currently possible with GitExtensions
You might want to use TortoiseGit for that kind of integration with the Windows Explorer.