Yes, this works as expected for me:
(defclass foosys (asdf/system:system) () (:default-initargs :default-component-class 'foo))
(asdf/component:module-default-component-class (make-instance 'foosys)) => foo
indeed. after Robert's mail i also tried this, and it worked, yet i'm seeing the error when i use :default-initargs, but not when i'm using a slot override.
it's a more convoluted issue involving our entire codebase that i'll need to investigate. sorry for the noise!
- attila