It's called a "shadow government" in European (?) parlance[0], though not to be confused with the term "deep state". That is, the opposition basically prepares a shadow government to signal to the public that, despite not being power, they have the qualified personnel ready to go on day 1 if they come back to power. The down side for MAGA when firing all these workers in all these agencies is that it gives the opposition the opportunity to organize a "department in waiting" for every agency that is gutted by gathering the most-qualified of the fired employees.
But just another billionaire doing this instead of an organized opposition is not ideal, to say the least. ex 18F workers should get someone they trust more in the mix.
Trump and Musk destroyed USDS and 18F. At worst Cuban is trying to salvage something from the wreckage.