What sane defaults are will change over the years.

Perl kept amazing backwards compatibility by adding extra statements to modify how it worked. So "use strict;", "use warnings;" and "use <other_newer_perl_features>;".

Both new code -- using the best OO system of the scripting languages, extendable syntax, etc, etc -- will run at the same time as most of the old and crufty stuff from before testing took over after the Millennium.