Nintendo has a saying describing their console philosophy that, roughly translated, means “lateral thinking with withered technology” (枯れた技術の水平思考) — that is, taking something old and limited, and doing something so unexpected with it that it feels fresh.
This applies just as well to break-out, genre-defining music hardware. For a sound to define a genre it must be distinct — crucially different in some way from everything that came before. Be it the rigid, electric beats of the 808 or the squelchy, octave-jumping arps of the tb-303, nothing had sounded like them before.
The “lateral thinking” part comes in when one realizes many devices of the time could have sounded like them. It wouldn’t have been a problem to patch something sufficiently 303-like on a minimoog or modular. Why wasn’t Wendy Carlos dropping acid riffs?
Because when a box can do anything, it’s hard to hear what’s new instead of what’s familiar. When faced with 10,000 choices, it’s hard to “think laterally” for every single one of them.
But just look at the front of a 303. You’ve got a step sequencer that you can only program long chains of notes on, the only “plocks” are accent, octave up/down, and slide, and the only knobs are resonance, cutoff, and the env mod thereof. It can’t help but sound like a 303. Using the withered technology of the time, Roland made something lateral enough to be new (whether intentionally or not is a whole other thread).
The same is true of the 101, 808, 909, sp-303/404… I’d probably throw the DX-7 in that boat, too, just to give Roland a break.
So I think that’s something to look for in future genre-defining gear. What’s forcing us to think laterally enough to build new sounds and is withered enough to be obtainable by the masses? The OP-1 is certainly distinct and lateral, but not withered. The Volkas are withered, but not lateral.
Something like the Syntakt, actually, is sort of on the line. Moderately lateral and almost withered. The Micro Freak and 0-Coast are the most promising examples I can think of. Of your list, I think the Rhythm Wolf has the most promise in this respect.