Ask HN: What's an e-ink tablet with SDK/toolchain for lag-free stylus and WiFi?

Hi HN, I'm keen to develop a self-hosted/offline-first notes taking program, with an integrated Zettelkasten system (see Roam/org-roam), and sync across devices. For the main notes creation phase, I currently use a Huion canvas tablet with my laptop - but ideally, I envision something like the Remarkable 2 or sort-of-similar tablet. I'm currently using FabricJS in the browser, but I'm not tied to this across devices - happy to develop native code.

The problem is I haven't found a suitable device yet. The Remarkable 2 has some toolchain/user code allowed, but apparently the GUI side is hacked/reverse engineered.

I've tried a Boox Note 3 with HTML/canvas drawing but the lag was insane, and the "e-ink" cheated by drawing a low-res segment before "painting it in" afterwards which was very jarring.

The in-build software for note taking in existing tablets are useless for me, as I don't want to export individual notes to PDF or save them on somebody else's computer just to sync.

So I'm looking for: 1) A tablet I can use outdoors (prefer e-ink-ish for reading in the evening) 2) Battery-free stylus (negotiable) 3) Developer friendly (must have) 4) Access to the GUI/Stylus without lag (must have) 5) Wifi access so I can sync with other devices 6) C/C++/Python/Java/Javascript would be great, but other languages considered. 7) If I can run Syncthing on it, that would just be amazing. 8) Ideally, no hacky/reverse-engineered stuff that's going to break with the next unprompted/accidental update.

I have emailed Reinkstone to ask them to test FabricJS (http://fabricjs.com/freedrawing), but they seem very busy at the moment and haven't gotten around to testing it. I have been badgering Remarkable and Kobo on Facebook since they keep advertising at me but no luck yet.

Thanks for any suggestions!