From looking at it, any filesystem that has it's modules in a core extension in /opt/tce in a remaster and is supported by blkid should work with the tc-config functions. Of course, untarring the modules into the remaster and then either depmodding or using an adjusted modules.conf should do the same.
But as ext4 is not supported at the present time, my advice would be to place the TC files and extension directory on another partition. Things move fast around here and tend to stay pretty current, so I would just hold tight for now.