Well the problem is that a large scale seminary effort located outside mainline China would be impractical, since there are by their nature more house churches relative to the number of the faithful than conventional parishes. Also using the Patriotic Catholic and Patriotic Protestant churches as entities to train leaders of the house churches would likely not work as the clergy of these entities are under close surveillance, to the point where these churches are not able to effectively meet the need the CCP insists they serve, and also that does nothing, for example, to assist the Chinese Orthodox community, which has been operating underground in mainland China since the the 1950s, presumably because Mao perceived ROCOR, which had operated the Chinese Orthodox Church after the rise of communism in Russia, as a threat to state security, although there still are Chinese Orthodox parishes operated by ROCOR in Hong Kong, Macau and Taiwan. So for all of these reasons, in order to ensure that independent Anglican, Orthodox, Calvinist and other denominations are able to operate in house churches in China free from government interference, and have educated clergy, I think the way to do it is to have only a handful of house church pastors leave the country for education abroad, and then have these pastors return to China and train, ordain and mentor additional pastors, who would rinse, wash and repeat, on a sort of cellular system. In this way entire hierarchies could be organized in a manner opaque to the PRC government and security forces.
Also, from an Anglican, Catholic and Orthodox standpoint, it is interesting to consider that historically there is a Patristic precedent for one bishop to ordain another in situations of persecution, without two co-ordaining bishops as is ordinarily required (since normally to make a bishop you need three bishops). A famous case of abnormal one bishop consecrations are those performed by St. Jacob of Sarugh during the severe persecution of the Oriental Orthodox of Antioch, hof what would become the Syriac Orthodox Church, since after St. Severus we stop seeing very many notable examples of natively Greek speaking members of that church or indeed the Coptic church. This is why the Syriac Orthodox are sometimes called “Jacobites”, because of a mistaken belief that all of their bishops were only ordained thanks to St. Jacob of Sarugh, excluding anyone else.
Likewise I seem to recall one of the Old Believer hierarchies of Russian Old Rite Orthodox deriving its apostolic succession from a single bishop of the Church of Georgia. This is also the theoretical case in the case of the United Methodist Church, since John Wesley was unable to deny, and at the same time prohibited under penalty of death from openly admitting, to the fact that he was consecrated a bishop by Erasmus of Arcadia, and regardless of whether or not that happened (which it did, although John Wesley’s doctrinal position was that it was irrelevant since in his view presbyters could function as bishops in extreme cases), he acted solus in ordaining Superintendent Coke for the Methodists in North America.
The point to all of this is that for those churches which want to operate in China and for the time being would be forced to work using the house church system, it would likely be expeditious to consecrate those clergy who were trained abroad as bishops and allow them to ordain the more senior house church leaders they trained, specifically those who they had trained to the point where they were qualified to train and supervise other house church pastors, as bishops. This would I believe, for churches with an episcopal polity, lead to a smoother transition from house church to parish when the communist regime in China collapses, which seems inevitable given Xi Jinping’s neo-Maoist crackdown on human rights.