I suppose its possible! The first product Midiman (Who still exist, as M-Audio) made was called (unsurprisingly) the 'midiman' and did fsk-timing-recorded-to-a-cassette the same way the mpu-401 did; Making the MM-401 was sort of a logical next step (implementing the intelligent mode and other stuff of the mpu-401 plus the fsk stuff from the original midiman)
If anyone is wondering what the FSK (which btw means "Frequency Shift Keying" and describes a form of digital data stored on an audio cassette using different frequencies for 0s and 1s) stuff did, I believe it worked like such:
The midi data for one channel (possibly multiple channels depending on some details i'm not sure about) gets stored, with no timing information in a stack in the ram of say an appleII; The appleII runs in a tight loop direcly reading the cassette input and checking which tone is playing. when the tone being played pulses the other state, a byte is popped off the stack and sent via midi to a device.
Tl;dr: Its like a midi file where the timing data is stored as sync pulses on a cassette tape, but the actual midi data is stored as a raw binary block on the computer itself. (or so I understand; I could be wrong about this)
"When life gives you zombies... *CHA-CHIK* ...you make zombie-ade!"