> Huh? Why "monolithic block of code"??? I'm perfectly happy with
> separating of functions - different filesystems are free to use the same
> implementation of RAID, LVM, etc - if their authors decide it's the best
> way to do things. Just as long as it's not exposed to userspace (or at
> least to user).
Well you seemed to imply it by saying you couldn't imagine it being down outside of the filesystem.
Permitting layers, I could imagine some specialised "meta" filesystem being feasible, that would give you a name space, that lets you tag directories and files with storage characteristics using more traditional type file systems as backing stores for bulk data storage. The real files might end up in a file hierarchy, spread over a number of volumes a bit like http proxy caches, to provide manageable chunks of RAID1, RAID0, RAID5, RAID10 storage, which can be increased (and freed) on demand by the Disk Management System.
The only thing is, how many ppl would actually need that? And if it were provided, how many would ever use funky "Save As" options, in applications, compared to the number who would whinge about excessive options, being confusing and unclean in their precious GUI?