Historically the "current generation" of e-ink displays are notoriously annoying to hack on with devkits being expensive and waveforms being available only under NDA. This was true 5 years ago, not sure if it's still true.

I've done a fair bit of tinkering with ePaper displays attached to little Linux and MCU boards, and it is not trivial. Few if any have touch overlays, the graphics APIs are usually at the level of: magic initialization happens in this opaque chunk of bit-bashing, then you get a raw framebuffer; have fun!

You absolutely could homebrew a touchscreen ePaper "slate" with a similar broad set of features, but much like the Libre laptops (Purism, Novena, etc.) it's going to be slow, power-hungry, and chunky compared to a complete consumer device like the reMarkable.

This may interest you; might not be what you were asking for. I haven't built one, but keep an eye on it and dream of free time to surface mount solder and poke around with it. The repo used to have a cost estimate and think it came out to around $100 but my memory may be fuzzy.

https://github.com/joeycastillo/The-Open-Book

It is not just a "white screen." The display is designed specifically for use as a paper substitute for writing/drawing. It actually feels like paper when using the stylus.