Does this mean Geos will never be possible with just the Kung Fu Flash?
Well, never say never. But it doesn't seem to be into near reach. Maybe it's quite impossible at all.
In the meantime you may have a look at GEOS 64 2.1e which was created to run from Cartridge. Please keep in mind that this version is not as versatile as the original GEOS 64 and that you'll still need a system disk that can be used with a drive (wether a real disk drive or emulated or sd2iec).