Our modern view of local congregations may not be synonymous with what existed in New Testament times. It is our Anglican approach to orders of ministry, as ordered in the New Testament, that has led to a diocesan ecclesiology. The locus of power and authority is in the bishop and the diocese. Congregations do not stand alone. They exist in a fellowship as is our godhead a fellowship of Father Son and Holy Spirit.
The bishop is really the minister of a diocese which is one community of believers worshipping in many places - originally in homes. The presbyters that have been appointed to local congregations are the “vicars” of the bishop - stand-ins. They and their congregations have no authority outside the bishop.
What has developed over the centuries into the Anglican Communion is a fellowship of Diocese that recognize and respect the authority of each bishop in a diocese. Some Diocese affiliate into Provinces but there is still a genuine respect for the authority of a bishop within the diocese over which they are appointed.
What has happened with GAFCON is that a group has said they can no longer respect the authority of a bishop within their own diocese. This is clearly the case as the church in Australia has had to develop a protocol for alternative episcopal oversight for those who will not submit to a bishop who is female.
Where this will ultimately lead I do not know, but it opens the door in my view for priests and congregations to seek alternative oversight because they disagree with the bishop’s view of the Atonement or their view of the authority of Scripture or any other theological controversy.
Another practice that is already evident in Australia is of congregations in one diocese “planting” like-minded congregations in another diocese with that congregation not being subject to the diocesan structures and authority where it exists.
I don’t see the evidence of GAFCON still recognizing and seeking to “work within diocesan structures.”
This new federation of “confessing” Anglican churches is actually moving away from what it means to be Anglican even though much of what they profess is catholic and orthodox. But they really can’t claim to be the true “Anglicans” and that the rest of the Communion are the ones who have strayed from the orthodox way.