The concept of Internet of Digital Reality (IoD) was introduced as the next level organization of cognitive entities following the concept of the Internet of Things (IoT) and Internet of Everything (IoE). As virtual-immersive environments are a fundamental component of IoD which allow human and non-human entities to interact in real time, the ability a wide range of communication modalities is crucial. This paper briefly presents the concept of IoD together with an overview of various I/O solutions for human users, with a focus on research directions and (re)emerging technologies in the near future.