Looks like a very similar solution as the Rotor 1x13 cassettes and freehubs. Theirs however let you use a normal shimano cassette on the freehub, with their 10T sprocket screwing onto the 11 tooth and an elongated lockring securing the whole lot to the freehub. The hub was spaced similar to if you use a boost adapter on a normal 142mm rear wheel, so slightly iffy chainline, but it works.
I have a vague memory of a company in the early 90's (maybe mountain tamers) selling a small sprocket for standard (7 speed?) cassettes of the time that replaced your lockring and overhung the axle a bit...kinda reminds me of that.