OK, let me shortly summarize what I understood.
1. Yes, MC is able to play non-DRM M4B files (like M4A, because it's only a different extension for the same audio format).
2. Yes, a support for audiobooks is possible in MC, but every user has to implement/customize it himself.
3. No, there isn't an out-of the-box support for audiobooks in MC like in iTunes (which comes with an own section and specific functionality).
4. No, there isn't a further support for audiobooks planned at the moment.
To be honest, I wasn't looking for a way to implement it myself. I was already aware of this possibility. I wonder to be the only user wishing this functionality from a media center product.
There was also no need for me to implement audio album support, so I was simply asking for anything comparable on your MC roadmap for audiobooks.
I even tried to limit the possible use cases to M4B files to reduce complexity, not asking for even more unstructured mp3 file collections for one audiobook.
So, this is now clarified for me.
Thanks,
Stephan