The page makes this assertion:
Wikipedia, for example, would be better served by a gated trunk model similar to the workflows used in w:DVCS development. In other words, "Kill the 'View Source' button" and always enable editing, even if the user's changes are saved to a sandbox and do not automatically update the public-facing default article contents. It is already possible to do something similar with Extension:FlaggedRevs.
However such a feature has absolutely nothing to do with the protection model. Moving protection into an extension doesn't help one bit to make this feature possible. In fact you could probably already develop it using the hooks we have available.