Let’s assume I create a new custom role by using the option “Make copy of” when creating the new role. I know that creating role this way will essentially copy the role you select and give it the new name you provide.
Now what if a new release of WordPress updates the WordPress role you copied from. This would mean that your new custom role will not have the changes made to the default WordPress role.
Would it be possible to have an option that would somehow keep your custom role in sync with the WordPress role that you copied from plus keep any changes you made to it?
In case you extend an initial role: make a copy from it, then add some additional capabilities, such synchronization would be achieved via multiple roles assignment to a user: initial role, 2nd role with additional capabilities. User will have a full list of capabilities as a result. Any updates applied to an initial role will be applied to such user automatically.
If you start from an initial role in order to narrow its capabilities list, then auto sync of new role with an updated initial role to difficult to realize, as you never know what to change automatically.
WordPress changes default roles very rare. It’s not too difficult to monitor such changes and add/revoke 1-2 capabilities manually after one of WordPress core updates was installed.
I do not see a need in a described functionality according to all of written above.