Pairing it with a low refresh rate is admitting defeat. There are already multiple products on the market with full-screen refresh beyond 30Hz; Dasung’s Paperlike is probably the best known, they don’t publish an actual figure but just say it’s almost as high as LCDs; I’ve found one place of no obvious credibility saying it’s about 40Hz. All this is with ghosting, of course. High quality rendering definitely takes longer, and I get the
impression from my reading and observations of a real device that bandwidth may play a part in that speed limit.
Partial screen updates can go much faster than that; reMarkable 2’s total latency from marker to screen update is around 23ms if I recall correctly, and I suspect (without confirmation) that it’s updating the screen at 200Hz, the sample rate of the marker.
In theory, yes, you can go down to 1- or 4-bit colour (and at 600dpi I think going hard monochrome and depending on dithering would be quite acceptable), but in practice software stacks are rather attached to 24-bit and don’t tend to like going below 8-bit. Especially general-purpose stacks—if you build something yourself from the ground up (whatever that means), then sure, you can generally choose your own path. There are certainly paths that make better use of meagre resources, but experience says they’re seldom taken.
I think you’re probably underestimating how much power pushing that many pixels and that much screen bandwidth takes. Such a device is feasible (provided they can manufacture a large enough panel with a tiny enough dot pitch), but not straightforward, and will have some significant tradeoffs. I’m not surprised no one’s trying anything even close to it.