Have you considered a dedicated writing machine? The AlphaSmart Neo2 is well regarded as a distractionless writing machine. They don't seem too hard to find.

Otherwise, if you really want vim and emacs, you might consider trying to put something together that can be always on. S3 sleep is low latency, and can be lowish power. Or get an early x86 chromebook and boot to freedos; chromebook because the firmware is small and doesn't do much; x86 because software compatability; early because the earlier ones are easier to run 3rd party firmware on for better use of non chrome OS; freedos because it's small and fast to start (assuming it supports the chromebook keyboard anyway).

What about an iPad? You open it (If you have the keyboard accessory) and it's ready instantly with the app you last opened. Something like iA Writer is very minimalistic with no distractions and everything is full screen. It's basically a white background with a cursor.

For some reason I’ve found iPad with keyboard one of the best ways to write. It seems to get fewer distractions than phone or laptop and has stickier “full screen” that’s harder to tab away from.

Sounds nice, what is the "keyboard accessory" you have mentioned? Does iPad really starts instantly after battery has replaced or drained to zero? For example, my Blackberry also starts instantly, but if replace the battery, the next start will be more than a minute long.

I'm talking about the "Apple Magic Keyboard for iPad Pro" but any Bluetooth keyboard should work too. If the battery is fully drained it shuts down and it'll have to start up (Couple of seconds). It isn't really an issue as a charge usually lasts you a couple of days, especially if it's just writing.

Is this similar to a computer in sleep mode. Actually, I think a computer in sleep mode won't need much energy.

Is it possible to be instant on/off? Yes. Is there a market large enough at support building such a machine currently? I would think no, people generally want more than a typewriter with a screen.

Early computers did turn on almost instantly but program load times from tape or disk was slow. Although in some instances I could say from direct experience that a c64 power on to text editor can be faster than a modern computer.

I believe back in the 80's the was some single purpose computers built with word processing, spreadsheet and other very basic office programs built in. These would be very fast but might not meet your idea of an OS.

Old systems that had cartridges, if you could find a text editor, also should be very fast. Again the idea of what you mean by OS may not be met.

I really want only typewriter. All I need from that OS is an ability to run vim or emacs or maybe any other text editor, but vim and emacs I appreciate the most. I don't reject modern technologies but in the world of super-smart and all-mighty devices, I am looking for one machine to be as stupid as possible.

I have the efficient p31 hynix nvme on my laptop. It only has 8gb of ram. I have it set to use Hibernate whenever i close the lid. It seems super fast, and then battery life is prolonged (no random sleep drain issues).

Why not use the hibernate command? It’s quite fast if you don’t have large amount of RAM in use.

Yeah I have the efficient p31 hynix nvme on my laptop. It only has 8gb of ram. I have it set to use Hibernate whenever i close the lid. It seems super fast, and then battery life is prolonged (no random sleep drain issues).

There is already a niche market for this, maybe the best example product is the Freewrite.

Is there room among the top ten for a purely mechanical typewriter?

Surely, the right tool for the write job does not make a Luddite.

Almost instantly

Can you measure that in milliseconds? And please share some data about your system.

Is having the computer be ready in a second or milliseconds really the bottleneck in the writing process?

Maybe I'm ignorant but it sounds similar to people writing their perfect static site generator instead of actually writing blog posts.

Your point is decent, it is definitely hard to find another people with similar desire, but I do not going to rid of my computers btw. Instead I am going to get an extra computer (a typewriter is considered as well) for my garage where energy shortages is a common and where I use to work at some technically-loaded hobby projects. That's why I afraid that the computer will interrupt my workflow via begging too much of my attention. So, I hope to exchange all multimedia options for instant power-up to end up with a typewriter with editing option and nothing more.

I think in that case an iPad might be a good companion as it has a long lasting battery, can be carried around and if it's a dusty environment it doesn't have big problems with that.

Would also make it easy to keep backups if you just take it back into your wifi/power area of the house from time to time to charge and sync.