We have two examples of "separated brethren" in the earlier history of the Church. In the New Testament, we get hints of the target market for the gospels: Pharisees and other Jews, Samaritans, Greek and Roman pagans, and everyone else. The controversy among the apostles in Acts resolves itself in the agreement between Peter and Paul that Jews and Gentiles will all be treated the same way -- they'll come in as individuals and families via parishes in a single missionary episcopal structure.
The second model, it seems to me, is the early heresies, which I understand at the 30,000 foot level via MacCulloch and others. Arianism is an example: it was attacked by Augustine and established as heretical in fourth-century ecumenical councils, but that didn't make it go away. According to Wikipedia,
During the time of Arianism's flowering in Constantinople, the Gothic convert Ulfilas (later the subject of the letter of Auxentius cited above) was sent as a missionary to the Gothic barbarians across the Danube, a mission favored for political reasons by emperor Constantius II. Ulfilas' initial success in converting this Germanic people to an Arian form of Christianity was strengthened by later events. When the Germanic peoples entered the Roman Empire and founded successor-kingdoms in the western part, most had been Arian Christians for more than a century.In other words, Arianism was a structure of beliefs that reinforced social and political arrangements, including who qualified to be members of the elite. Protestantism has served a similar purpose in the UK and parts of Germany, for example. Arianism eventually collapsed after several centuries. For whatever reason, the Holy Spirit seems to have guided the Church in large measure simply to bypass Arianism, as it seems to have taken no special measures to make itself appealing to Arians.The conflict in the 4th century AD had seen Arian and Nicene factions struggling for control of the Church. In contrast, in the Arian German kingdoms established on the wreckage of the Western Roman Empire in the 5th century, there were entirely separate Arian and Nicene Churches with parallel hierarchies, each serving different sets of believers. The Germanic elites were Arians, and the Romance majority population was Nicene. Many scholars see the persistence of Germanic Arianism as a strategy that was followed in order to differentiate the Germanic elite from the local inhabitants and their culture and also to maintain the Germanic elite's separate group identity.
Most Germanic tribes were generally tolerant of the Nicene beliefs of their subjects. However, the Vandals tried for several decades to force their Arian beliefs on their North African Nicene subjects, exiling Nicene clergy, dissolving monasteries, and exercising heavy pressure on non-conforming Nicene Christians.
The apparent resurgence of Arianism after Nicaea was more an anti-Nicene reaction exploited by Arian sympathizers than a pro-Arian development. By the end of the 4th century it had surrendered its remaining ground to Trinitarianism. In western Europe, Arianism, which had been taught by Ulfilas, the Arian missionary to the barbarian Germanic tribes, was dominant among the Goths, Lombards and Vandals). By the 8th century it had ceased to be the tribes' mainstream belief as the tribal rulers gradually came to adopt Catholicism.
It seems to me that Protestantism is in a similar process of collapse. The ordinariates are a relatively expensive measure that has had minimal appeal, but they have a downside in creating the appearance of failure.
In addition, the Church's priorities for evangelization are not with Protestants -- they're with secular materialists, the unchurched Unitarian transcendentalists, and Mahometans. Protestantism, especially the main line variety, is collapsing of its own weight. As the maxim goes, when your enemy is destroying himself, don't get in his way.
