It’s interesting reading that the reasons for jailbreaking a kindle are so trivial, amounting to adding some minor functionality to reading books and not much else.

Kobo jailbreaks from back in the day gave you root on a stripped down Linux install, complete with telnet ssh and ftp. You could even install python and essentially do anything the cpu/display permitted. Another cool aspect with those older kobos was that they had two microsd card readers… one hidden inside the enclosure that contained the OS, accessible without even needing a screwdriver.