I was going to post that the same sort of mandate had applied to Ada, and was eventually abandoned. I remember Ada the mandate, but I recall obtaining waivers from the mandate (on specific DoD programs) before 1991. I predict that this mandate will suffer the same fate as the previous one.

A quick search confirms my memory:

The DoD Ada language mandate, which required the use of the Ada programming language for most Department of Defense software projects, was established on March 30, 1987 through Department of Defense Directive 3405.2.

https://dl.acm.org/doi/10.1145/255471.255599