I think Clark was justified in deviating from Ossanna.
The prime rationale for allowing removal of read-only registers is
uniformity--a powerful argument. It simplifies documentation and
relieves a burden on users' understanding. It probably simplifies the
code, too.
This kind of special-casing is AI in the service of some perception
that "no one would want to do that.". If "that" is the clear meaning
of some specified action, then so be it. We are not dealing with
physical hazards here.
even if they don't screw up the formatter
internally,
they will become unrecoverably useless for documents
and macro packages,
The same argument could be made about \applying .rm to any standard
request, and I would disagree for the same reason as above. (A
disappointing experimental discovery in this regard: .de seems to be
immune to removal.)
A change that I *would* welcome is warning about writing into a
read-only register. (Also make .rm work on .de--a near reversal of the
original proposal.)
Doug