In the last five years, we witnessed the shift from the vision of the Internet of things (IoT), to an actual reality. It is currently shifting again from specific and single applications, to larger and more generic ones, which serves the needs of thousands of users, across borders and platforms. To avoid losing the personification of applications, on account of genericity, new approaches and languages that use generic knowledge as a steppingstone, while taking into consideration users and context's specific and evolutive needs are on the rise. This chapter aims to provide a framework to support the creation of such approaches (DSPL4IoT). It is later on used to asses notable IoT specification approaches, and extract conclusion of the trends and persistent challenges and directions. An approach for the specification of Natural Language (NL) requirements for IoT systems is also provided to assist domain and application engineers with the formulations of such requirements.