Corinna isn't being made to disallow Moose or Moo (or Object::InsideOut, Class::Accessor, or whatever else) from working. It's being made to have a sane default in the language that's a bit more modern and more opinionated than blessed data structures and a bit more performant and available than something that sits wholly outside the core.

Could all the object models on CPAN continue to work without Corinna? Yes. Could they continue to work just the same alongside Corinna? Yes, excepting some might have a keyword collision or two to clear up. Could they embrace Corinna and offer what they choose in addition to what Corinna brings into core? Also, and emphatically, yes.