In the last decades, Model-Based Systems Engineering (MBSE) has received significant attention, leading to standards such as SysML. SysML is due to a recent and radical update, breaking the dependence of its specification from UML, and leading to the development of two languages: KerML, which provides a top layer of general constructs, and SysML v2, which specializes KerML for systems engineering. In this paper, we analyze the formal and real-world semantics of the proposed KerML and SysML v2 specifications, and draw implications for their improvement and further development. Our attention is focused towards key constructs of the languages. We also examine the approach taken in the specifications to deal with dynamic aspects, which is inspired by the ‘four-dimensionalist’ view.