You could create a microflow that retrieves the current accound based on the Account.ID = $currentUser.
Why do you want to generate an entity that inhereits from the current user? What is your goal?
We need to assign access rights to users on specific objects, i.e. we need to implement access rights managment. For that we need to represent the users, and we also want some additional attributes. So our idea was to use a specialization of System.User (and Adminstration.Account). But this means that the System.User objects that are generated (when users log on for the first time, I assume) need to be turned into this specialization.