This is a great point. Back when I was checking I think I was underwhelmed by the customization ecosystem for kobos but now I’m not sure what was stopping me/made me reconsider.

Upon further inspection there is also the Pine Note!

https://news.ycombinator.com/item?id=46283016

https://pine64.org/devices/pinenote/

It’s quite pricey but certainly more straightforward in its offering.

Kobo is the cheaper and has a color option and is likely slightly less hackable.

[EDIT] Ah, I think this is what I found:

https://github.com/Quill-OS/quill

Kobo’s switch to secure boot made things harder for Quill which seemed to be the only custom OS.