There is a discussion here which is suggesting that the Wikipedia Books function be withdrawn. The RfC concerns user interface hooks to the collection extension and the discussion has broadened into the whole Books namespace and this software. You are invited to contribute.
I understand that PediaPress are, or were, heavily involved in maintaining this extension. Anybody who knows their full relationship with the WMF would also be more than welcome to give a clarification, as the upload link to their PoD service is also being criticised.