Is a MOP (like CLOS) going to bring substantial advantage to extensibility? My intuition says yes, but I can't test this hypothesis without thousands of plugin developers. Has any (meta) study even been done?
I think Elisp already implements a lot of things that CLOS would give you, like around method combinators (with defadvice, if I remember correctly). It's probably more ad-hoc, and you might want some extra customizations on top, but I'm not sure.
