Are you aware of IMDisk? (http://www.ltr-data.se/opencode.html/)
It has more options than TrueCrypt for container creation, including floppy/DVD emulation, and of particular use to me, it supports memory-based file systems. There is no built-in encryption, but there is a proxy interface which looks like it would permit encryption to be added on a per-container basis.
I'm not sure if the interface would permit implementing a new file system, but it's worth a look. A decent SSH-FS implementation for Windows would be great.