Literature

They haven't really advanced a whole lot, unless you want an android tablet with e-ink and deal with the annoyance that will bring or are looking for an eink tablet to write on. Newer ones aimed primarily to reading are now usually water resistant, have non-recessed screens, and audiobook support with the exclusive service each ereader company is provided by (kobo only has kobo audiobooks, kindle only has audible books etc) so the technology hasn't evolved a whole lot unless you want to detangle yourself from the Amazon ecosystem. There are android e-ink tablets, but most them are unfortunately made by Chinese companies that not only require you to manually enable the android app store, but there's pretty big privacy concerns and just general shady business practices amongst nearly all of the few that operate in that niche market (especially amongst Boox, they have paid people to write fake reviews)

There are some color ereaders but the technology isn't really ready for general use, its very finnicky and has a bunch of issues when used in consumer ereaders. Writing based eink tablets are excellent though, if that's something you are into.

I personally have kept my 2015 kindle and as long as its still running I'm gonna stick with it personally.