In this article, we envision a hybrid opto-acoustic network design for IoUT. The software defined underwater network (SDUN) is presented as an enabler of hybridizing benefits of optic and acoustic systems and adapting IoUT nodes to the challenging and dynamically changing underwater environment. We explain inextricably interwoven relations among functionalities of different SDUN layers and analyze their impacts on key network attributes. The NFV concept is then introduced to realize application-specific cross-layer protocol suites through an NFV management and orchestration system. We finally discuss how SDUN and NFV can slice available network resources as per the diverging service demands of different underwater applications. Such a revolutionary architectural paradigm shift is not only a cure for chronic underwater networking problems but also a way of smoothly integrating IoUT and IoT ecosystems.