It's a bit the same here - the kobo is still a normal functioning Kobo. Only the kernel has to change to allow USB OTG mode, and you can switch between custom and stock one. By the way, the libs I used here works on remarkable too, so it's just a matter of compiling the software and finding a matching kernel.
See for instance this post by Nick Temple: https://nicktemple.com/blog/remarkable-keyboard/