I also think of Jeremy Bell, who did and shared the ScrubBoard – also a cassette tape thing. He did a Kickstarter with it and it failed unfortunately. ( post )
Also in the realm of cassette tape audio generation devices is the HC-TT from Landscape.
Either of these could be blended into this sort of system, as they all take and amplify signals from magnetic tape heads.
So is the Cassettone in stereo ? How about using all four tracks on a cassette, with a four track head ?? Then mix that down, or allow quick cuts between heads with an LFO signal or two. This would all be easy using modular gear.
ADDED : Alternately there is a speed controllable four track modular cassette player device called Noodle Rider. ( post )