Is it possible to dune utop mylib load a library in "promiscuous mode" which would ignore the .mli interface files and expose the internals, like values or types not listed as part of the public interface?
In effect, loading utop "from within" the implementation, and not "from outside", issuing standard open commands with abstraction enforced by the public interface.
This is not possible. You can open a ticket on the github repository of dune to ask for such a feature.