It appears that both Itcl 3 and Itcl 4 have
this command access to a method in place.
In Itcl 4, though, every Itcl object is a
TclOO object and every Itcl method is a
TclOO method, so when you try to invoke a
TclOO method (even through a command backdoor access)
on a TclOO object that lacks that method, the
access restrictions of TclOO catch that and
report the error.

I don't have a strong sense whether this is
stopping something that was never a good idea
to begin with, or whether it is exposing that
TclOO and Itcl have even more deeply fundamental
disagreements about their very models of operation
than was ever appreciated, and that in a deep
sense the Itcl 4 project of building Itcl on top
of a TclOO foundation is just unworkable.