[$] Policies for merging new filesystems

In a filesystem-track session at the 2026 Linux Storage, Filesystem, Memory Management, and BPF Summit, Amir Goldstein wanted to discuss his proposed documentation on adding new filesystems to the kernel. There are a number of unmaintained and untestable filesystems already in the kernel, which are a burden to VFS-layer developers who are trying to make sweeping changes, such as switching to folios and the "new" mount API. Goldstein's document is an attempt to head off the addition of filesystems that may increase that burden down the road.