Yes!
My most recent search for any developments in e-ink laptops was literally yesterday. My understanding is that current e-ink screens are not technically limited to low refresh rates, but are artificially limited to save power. (I think someone hacked their e-reader to run linux at fairly high refresh rates?)
Regarding dumb terminal, if your situation allows you to I feel this is currently one of the better options available. One problems is you still need to browse the web locally and graphically and use various tools not available using emacs and/or the command line. And when internet connectivity is not available.
Maybe I don't quite understand what you want then. If you want minimal productivity focused machine just setup your system that way. Install the tools you need and call it a day?
I'd just grab a used thinkpad, chromebook, whatever and treat it as a dumb terminal. Pretty much how I used my laptop these days, ssh -X to a powerful machine and go. emacs --daemon / emacsclient (and of course a couple tmux/screen sessions) means I never lose my state.