Actually registration is open to everyone now by simple form submission. So actually, any one developer could get any change they wanted merged. All they need to do is trivially register a second labs account.
Okay, but current situation is also a problem, because with it reviewing and merging takes much more time. And as I've said, I think most extensions aren't as important as the core, and limitting approve for them to core developers is just a waste...
Maybe you should add some group similar to previous (SVN) "commit access to extensions", so a wider group of people could merge changes to the extensions?