This video (in french) says future beluga will be probably an a330 NEO derivative, the program will be announced in spring 2015. At least 5 Beluga NEO will be built, and they announced an EIS in 2018. For me 2018 is little short because a330 NEO EIS is Q4 2017.
To industrially accompany the A350 XWB ramp-up and other aircraft production rate increases, Airbus took the decision to launch the development and production of five new Belugas.
The new Beluga will be based on the A330 with a large re-use of existing components and equipment. The distinctive looking lowered cockpit, the cargo bay structure and the rear-end and tail will be amongst the items which will be newly developed.
The first of the five new Belugas will enter in service in mid-2019. The existing Beluga fleet will operate in parallel, and will be progressively retired through to 2025.