The use of lov_desc to store the default filesystem layout is restrictive as new layout types are added, and prevents functionality such as using "lfs setstripe" to set a default pool for the filesystem.

The default layout xattr should actually be stored directly on the filesystem root inode, instead of just virtually using that as meaning "store the default layout into lov_desc". That would avoid any feature problems as new layout types are added in the future, since it will just be storing a layout xattr.