Right now I'm using an old rooted (and beat to hell) nook simple touch for reading a lot of theory. I'm hoping to upgrade to a Kobo one day once I can talk myself into spending the money.
I'm keeping an eye on this, might end up being a decent option once it matures a bit https://www.pine64.org/pinenote/
I've always been a fan of the things pine is doing, my biggest want in an e-reader is battery longevity. If I can get a week or more in of pretty consistent reading I'd be really happy. The pine note definitely has a faster processor, which makes me think it wouldn't last quite as long.
But of course the openness of it would be a huge huge plus regardless.
Yeah for sure, I think battery life is really the key aspect of an ereader as well. From what I've seen the screen is what tends to eat up the battery the most, a faster CPU doesn't necessarily mean a lot of battery drain since it would generally just be idling anyways. And yeah, I'm a big fan of open hardware. Would be amazing if a viable ecosystem develops around that going forward.