As near as I can tell, the only visible behavioural change with Daniel's patch (updated as per my last comment) will be that the two error cases noted above (i.e. when an explicit metaclass or the first parent type's metaclass is not the most derived metaclass) will now correctly invoke the real metaclass immediately, instead of first traversing up the chain to type(), which then jumps all the way back down to the most derived metaclass.

The "new" special case is actually just a matter of preserving the current behaviour in the one situation where that is the right thing to do.