I'd just like to give a description of some of our use-cases which might not be totally reflected in standard regression tests (maybe they should be somehow).
What I know is that we depend heavily on immutable-systems behavior in production (e.g. for making pre-built Gendl distributions which won't try to re-compile and re-load Gendl and its dependencies on top of an image which already has them built-in, when quickloading other systems which have :depends-on :gendl).
We also depend (daily) on the monolithic-compile-bundle operations for making builds which don't end up including asdf themselves (but our builds do include uiop).