Which of the following is NOT a key requirement of an ERISA qualified plan?

The correct choice identifies a requirement that is not explicitly stated as a key guideline of ERISA for qualified plans. While having diversified plan assets is generally advisable for risk management and sound investment practices, ERISA itself does not mandate that all plans must diversify their assets. Instead, ERISA focuses on protecting participants' benefits and requiring prudent management of plan assets, which may include diversification as one method but is not a strict requirement.

The other options represent fundamental principles under ERISA. The prohibition against the diversion of plan assets is crucial to ensure that the funds meant for retirement benefits cannot be misused or diverted for other purposes. Operating for the exclusive benefit of employees and beneficiaries emphasizes the need for plans to prioritize the interests of those they are designed to serve. Lastly, the permanency requirement ensures that plans are intended to operate on a long-term basis, providing a reliable benefit structure for participants. These elements underscore the overarching goal of safeguarding retirement benefits under ERISA.