> Were you thinking of something like the old Zipslack?

ah yes, UMSDOS.  history.  languishing from lack of interest.

from wikipedia.org/wiki/FAT_filesystem_and_Linux
> The convention for such an installation is for the Linux root directory to be a subdirectory of the actual root directory of the DOS boot volume, e.g. C:\LINUX . The various Linux top-level directories are thus, to DOS, directories such as C:\LINUX\ETC (for /etc), C:\LINUX\BIN (for /bin), C:\LINUX\LIB (for /lib), and so forth. The umsdos filesystem driver automatically prepends the C:\LINUX\ to all pathnames. The location of the Linux root directory is supplied to the umsdos filesystem driver in the first place via an option to the loadlin command. So, for example, for the aforegiven root directory loadlin would be invoked with a command line such as loadlin c:\linux\boot\vmlinuz rw root=c:\linux .

next question, i wonder if a similar ability, for linux to boot its
root in a subdirectory, is available in other environments, eg ext3,
or HFS+, and if any distros and/or installers exist that make use of
that?  or what the syntax would be with a root= argument that already
specifies a UUID?