There has been much talk about a file system that would be compatible with Microsofts implementation of NTFS. There has also been discussion about using something like the ext variants of filesystems, so here are my thoughts:
Option 1 - Write an EXT3 - NTFS VFAT translation driver to allow ext3 to be the underlying filesystem.
I believe Mac OS X uses something like this with the way it can translate Mac OS X:Applications:Utilities into /Applications/Utilities.
Option 2 - Build your own proprietary filesystem incorporating things that people would like in the filesystem.
Option 3 - Build a file system but include features in the operating system that can be turned on and off like Compression or journaling.
Option 4 - Build a filesystem that encrypts itself throught the kernel or a program on the system with a public and a private key, kind of like SSL.
Option 5 - Keep the same file system intact, write a driver that allows users to encrypt a "folder" which is actually a file on the drive, when a user double clicks on a file the folder is either mounted based on a ticketing system or credentials, or, asked for a master password or a password that will give certain but not all priveleges.
Personally this would be my choice.
Tell me what you all think.