There is a proposal to Suppress rendering of Template:Wikipedia books on the English Wikipedia.
The accompanying discussion is suggesting that support for the longstanding PediaPress print-on-demand service should be removed because it is a pay-for service. I am sure that the WMF have some arrangement with PediaPress about this, and the last I heard PediaPress were also working on a replacement PDF renderer. Then there is Dirk Huenniger's MediWiki2LaTeX which is currently hosted by wmflabs at both http://mediawiki2latex.wmflabs.org/ and https://mediawiki2latex-large.wmflabs.org/ . Although the current proposal does not affect them immediately, it is also being argued that no support for any external services should be given. That would reduce the current Wikipedia Books function to nothing more than passive reading lists.