This is why I'm leaning towards the Note Air. The Kobo Elipsa is coming out soon but it syncs with Dropbox only.
It runs Android. You can just sync things through the cloud provider of your choice. Put the Dropbox, OneDrive, NextCloud etc. app on and just download it from there.
Most eReaders don't have upload by email just Kindles and that doesn't let you send a more recent better formats like KFX or AZW3, just ancient mobi. Ditto Bluetooth.
And guess what? At least with Android phones "Nearby Share" works too (although that may require setting up Google Play Store.
Apart from Kindle, Firefox and safari books online reader?
I’ve found that 3rd party drawing apps don’t work well with the screen.
The fact it runs Android is vastly better than some custom software (like Kindle and others) because of this reason.