(See parts I and II)
Step I in workable solutions towards Protestant unity is to redefine sola scriptura across Protestant boundaries that will get everyone on the same page on exactly what is authoritative. Ideally (though I did not discuss this), such a redefinition would also include a theory on the nature of inspiration and resolve any issues about textual variations within the canon, including potentially "uninspired" parts - like Acts 8:37 or the alleged "extra" ending to Mark. Step II was to figure out a way to overcome the diversity of interpretations in such a way that Protestant groups are able to fully recognize other group as legitimately Christian. This would likely require an abandonment of key distinctives in some, or many, areas and a near total ecclesial & theological reformation of some churches.
Though it may sound a little odd, Step III is figuring out how we are going to view history, because quite frankly, Protestantism is departure on many points of Christian history. Some of these departures are major and some are minor, but any way we look at them, we have to have a comprehensive way of receiving and interpreting history. I think the majority of Christian sects & denominations believe in a specific Golden Age of Christianity. For some, this age could only be during the life of the Apostles. When St John finally died on Patmos, the Golden Age ended and thus began the Church's long slide into corruption and apostasy. For other groups, the first 4 centuries are normative and they may accept some of the Ecumenical Councils as authoritative (to what degree varies by group). There is a continuum here, with Catholic and Orthodox on one end (who arguably don't believe that, in essence, the Golden Age ever really ended) and very strict Protestants on the other that may even suspect some of the teachings that cropped up during the Apostles' time.
As I said before, history is important because Protestantism departs from historic Christian thought in many areas. We are not liturgical, sacramental, hierarchical (for the most part) or overtly mystical. We believe in sola scriptura, though no such doctrine was ever embraced by the church-historic, reject many sources of authority early Christians fully accepted, and we are, quite frankly, inherently schismatic. Read through the earliest Church Fathers (those most likely to be favorably considered across the spectrum), and you will see an emphasis on unity, mutual submission and loving cohesion that seems impossible to achieve in our day and age, and that is not the focus of the majority of Christians. Early Christians viewed the Church as the mediator of their faith, in that the only true experience of Christ was found within His body. We tend to hold similar views about the Bible, and not the church, because we find the church intrinsically untrustworthy. It is only a human endeavor, and one that does not appear to be specially favored by the Holy Spirit, at least not the same way Scripture is.
So we have to figure out exactly what is normative for us. If a belief in sacarmental worship can be proven of the earliest Christians (and I think it can), should we change our services and your theology to conform to this historical standard? If the early church embraced a clear hierarchy of male-only leadership, should be conform to that as well? And perhaps the real sticking point - if the early church regarded extra-biblical material as authoritative, how do we deal with that? We have left history unengaged for too long, simply assuming we are modeling ourselves after NT worship, but this is not the case. We may have captured certain parts of it, and we may be doing a good job of what we're doing, but we need to figure out if it is what we are supposed to be doing.
Step III is developing a consistent view & interpretation of history across Protestantism. One that deals with questions of worship & ecclesiology, extra-biblical authority and the sacraments.