> Traditional filesystems are hierarchical, slow to search, and don't natively store all of the metadata we need

I don't know what he means by "traditional", but Linux native filesystems can store all the metadata you'd want.

> Why can't I have a file in two places at once on my filesystem?

POSIX compatible filesystems have supported that for a long time already.

It seems to me that all the things he wants are achievable through Plan9 with its existing API. The only thing missing is the ton of elbow grease to build such apps.