Checked that noone in Quicklisp seems to be using it.

Deactivate some stateful datastructures that depend on interface;
probably nobody uses them, and they ought to be merged into cl-containers or such.

Define a define-interface wrapper to defclass.
vector-bind, split-list. Boxes.

so you can (:use :pure :cl) without the need for :shadow

Stop using structure-class, it only makes it harder to use mixins.

Experiment with multiple-inheritance of pure interfaces and
with packages for interface namespace.