* PDF reader
* epub reader
* well-maintained paged-media mode Web browser (well-maintained meaning timely security patches for the browser and the base system)
* no app, just standard MTP over USB and whatever the Bluetooth file transfer protocol is called
* reasonable privacy stance (not collecting what documents are read)
When looking for the above, which doesn't exist, I settled on Sony Digital Paper (DPT-RP1) instead of ReMarkable. (My recollection is that the Sony device had a larger display and didn't assume a cloud component, which could shut down.)
Sony has the hardware side solved albeit in U.S. Letter size instead of A4. However, of the other points, it only does PDF.
Sadly, despite being based on Android 5, which meant they could have gotten the standard file transfers for free, Sony disabled that stuff and forces the use of their Windows and Mac app to load the PDFs onto the device. At least back when I bought the device (which was before the GDPR came into effect), the terms of service for the app were unreasonable: The terms claimed the content of the PC running the app as fair game for telemetry. Nope, nope. I've never connected the device to the network and I run the app in a manner that blocks it from accessing the network. One shouldn't have to take steps like this. The app and the terms for the app make even less sense considering that the marketing target of the device is doctors and lawyers, who even in the U.S. have specific document confidentiality obligations.
Sadly, I have no idea what kind of business model would enable a well-maintained paged-media mode Web browser. Taking an existing Web engine and making its print-oriented paged-media capabilities work well in the interactive case would be a major project in itself. And top of that, actually keeping up with security patches would be hard work. (I have used a continuous-media Web browser on eInk, and it's not a good experience.)
Anyway, I wouldn't go back to not having a Digital Paper device, but I feel dirty about Sony having gotten my money despite me having to deal with their PC-side app and its terms.