I have said on more than one occasion that Internet connectivity makes the CPS V methodology inadequate. The V methodology works top down for design, then bottom up for implementation, forming a V. It implicitly assumes that the specification is static, giving a known target for the end of the V. The changing threat from the Internet undermines that assumption.
However, we should keep in mind that many CPS systems make use of software from the IT world, whether it be licensed or open source. IT developers can no longer assume that their customers are solely from the IT world. They need to take into account the requirements of cyber-physical systems. To satisfy those requirements, they should adopt the more stringent verification and validation approaches embodied by the V methodology.
Many software IP modules are developed relatively independently of applications. A V-methodology-based approach would condition the release of these modules on validation within some exemplary systems. System-integrated testing from both IP and CPS domains would help to shake out bugs in both the implementation and specification.
Agile software development emphasizes fast development of disposable software. That approach makes sense for some domains. But long-lived modules require a different, more deliberate approach. The confluence of IT and CPS encourages us to invest in the careful design and construction of building block modules.