Artwork

Yes they can, via images embedded in their ID3 tags. This is supported by a huge array of players in terms of both physical hardware and software.

Keep your place

Yes they can, via many players (including both VLC which is what I use, and also my car stereo).

Sync across devices

This much is true, at least in the players I use. There's probably a solution with some specific player somewhere.

But specifically for audiobooks, I don't... need... to play across multiple devices. I listen via only two methods: My headphones (which are driven by my phone) and in my car (which works with my phone). I only actually use one player. It goes with me everywhere. Ours go with most of us everywhere; we're naked without 'em.

If your use case requires a networked solution, you do you. I'm just saying, don't automatically get blinded by how the Streaming Era has kind of fucked up everyone's brain.

Edit: Downvoting me doesn't change the fact that what you said was false.