I hope that Christians can be united in the belief that all (believing) Christians are part of the same universal body of Christ - brothers and sisters in Christ, traveling towards the common goal despite disagreements about some details.
Being united into one organization is not realistic and not necessarily even the best option. It is unrealistic to hope that the old churches would abandon doctrines that have accumulated during their long history, or that all younger churches would adopt all the doctrines of the old churches as disagreements about some of these doctrines may be the reason why the younger churches exist as independent organizations. Instead of hitting the head repeatedly to the wall, root-level cooperation, mutual respect and an acknowledgement of belonging to the same body of Christ would help a lot. There is more that unites us than what separates us.