The closest I can think of is the Hemingwrite typewriter which has an e-ink display and is portable in some sense. At $342, I hope it's more than a toy.

https://www.kickstarter.com/projects/astrohaus/hemingwrite-a...

Edit: oops! They have a new website and a new product that fits your request more closely.

https://getfreewrite.com/products/freewrite-traveler

But that's really a typewriter. Which is somehow good if you just want text, not code. And here's the problem: these things belong to consumer segments so narrow that I don't see them getting the attention I'd like.