Which of the following is NOT a typical challenge in RAD-based development?

In Rapid Application Development (RAD), the focus is on quickly developing functional prototypes and iterating based on user feedback, which inherently presents certain challenges. One of these challenges is indeed the postponement of risk assessments until after the development phase is complete. In traditional development environments, risk assessments are part of the planning and risk management activities prior to the actual development work. However, in RAD, the flexible and iterative nature of the process often leads to a situation where risks may not be thoroughly analyzed upfront but instead are identified reactively as issues arise during development.

The other options presented align more closely with typical challenges in RAD. For instance, a lack of complete requirements specification is common in RAD as it emphasizes iterative prototyping over extensive documentation. Similarly, time-boxing the development process is a core characteristic of RAD but can be a challenge as it limits the time available for thorough testing and refinement. Lastly, the issue of reusable test scripts for regression testing can also be problematic in RAD due to the frequent changes and iterations made to prototypes, making it difficult to maintain consistent test scripts.

Thus, the correct identification of the choice regarding postponing risk assessments aligns well with the challenges characteristic of RAD, making it the accurately chosen response.