Kobo and Kindle both run Linux too. Kobo still updates every single model they've released except for the first two non-touch models and the 5" mini stretching back a decade. And Amazon is pretty good with updates too.
Kobo is pretty similarly hackable to the Remarkables but they are not nearly as open and free as the Pine stuff. I take a look at what remarkable has updated, and they just still haven't gotten ePub support anywhere close to where it should be. I belive it technically converts ePubs to PDF and displays that?? With large books taking minutes to change font sizes. That to me has completely turned me off their devices. Writing may be better but reading is IMO equally important for devices like these.