Preferring composition to inheritance is hardly unique or new. However, having that designed into the language is far less common than it should be.
The more general ideas that underpin a composition implementation are the abilities to access class/interface metadata at compile time and to generate code programmatically at compile time.
Every project has friction between members, disagreements,
conflicts over style and philosophy. These social problems
are counter-acted by the fact that no large project can be
accomplished otherwise. "We must all hang together, or we will
all hang separately." But the expressiveness of Lisp makes
this countervailing force much weaker; one can always start
one's own project. Thus, individual hackers decide that the
trouble isn't worth it. So they either quit the project, or
don't join the project to begin with. This is the Lisp Curse.