Dang, yeah, this is the opposite of what I had in mind

I was thinking, like, a couple hundred dollar Kindle the size of a big iPad I can plug into a laptop for text-editing out and about. Hell, for my purposes I'd love an integrated keyboard.

Basically a second, super-lightweight laptop form-factor I can just plug into my chonky Macbook Pro and set on top of it in high-light environments when all I need to do is edit text.

Honestly not a compelling business case now that I write it out, but I just wanna code under a tree lol

I think we're getting pretty close to this. The Remarkable 2 tablet is $300, but can't take video input and software support for non-notetaking is near non-existent. There's even a keyboard available. Boox and Hisense are also making e-ink tablets/phones for reasonable prices.

A friend bought it & I had a chance to see it in action.

It is nice for some very specific use cases. (They're in the publishing/typesetting business. It's… idk, really depends on your usage patterns.)

Other than that, yeah, the technology just isn't there yet.