What problem does this address?

Right now, PostLockedModal is considered a crucial component of the editor and hence its tightly coupled. But with upcoming collaborating editing work in Gutenberg, this would change and since initially this work would be done outside in a plugin, we need the ability to cleanly unhook PostLockedModal.

What is your proposed solution?

Decouple it and make it use Gutenberg's API to register itself registerPlugin(), so that externally, we can cleanly remove the component.