The last point is a quibble and you know it. I write in the popular English of my day about a book without an original title translated from koine Greek. I think we can chill out and let the 's' slide.
Not a quibble. It is the correct (shortened) name for the book in English. Pick up any English Bible. You will not find one with the name Revelations. And, let's not forget that the title is taken from the first line of the text: 'The revelation of Jesus Christ....'
I don't mean that the text of the individual books wasn't finalized (that's not quite the can of worms I meant to open)-I mean that the particular books which make up what we know as the New Testament were not compiled into their present number and order until the 2-300s.
Not entirely correct. The Greek document underlying the Muratorian fragment is widely accepted as being composed mid-late 2nd Century. The correlation of that canon with the writings of Irenaeus of Lyons demonstrates that the core of the Christian NT was widely established by AD 200. There was some debate as to particular texts (for example III John, I Clement, Shepard, Revelation unto John, Revelation unto Peter, Didache). The councils of the Third and Fourth Centuries merely confirmed what was already being practiced.
But there was variability sufficient to generate controversy, and if I may indulge myself to imagine that the OP's point of divergence took place, I can give my speculations as to what that scenario might entail.
Minor controversy. Again by the time of Irenaeus, Christian writers were defending their beliefs by quoting what they regarded as Scripture. Even then, the controversy was often over what should or should not be read as part of the worship service.
I think it was one of the Peters I was thinking of. OK, since there were so many, then enlighten us as to which of these might slide into John's place in the canon, and what the religious-cultural effects of each might be.
The (Greek) Apocalypse of Peter had the best chance (really, the only one). Clement of Alexandria and the Muratorian explicitly named it Scripture. Methodius, while not explicitly naming it, identifies its teachings as Scripture. It was tied to the somewhat Docetic Gospel of Peter, and this may be why it was ultimately excluded. Its chances are also damaged by its claims that its teachings should be kept secret. It seems to indicate that the Father, not the Son, will judge the world. This places it in conflict with other canonical books, but its parallels with II Peter might offset this. It also draws on Platonic, rather than Jewish, imagery regarding the afterlife. It also includes connections to Pythagorean thought. Of course, the fragmentary nature of what is known makes it difficult to completely evaluate it.
The (Greek) Paul is clearly a late written expansion of Peter. No chance.
The Coptic Peter and Paul as well as both James are clearly gnostic and never had a chance.
Thomas was a later Latin version of John. No chance.
I am not overly familiar with Stephen, but I think it is a gnostic text as well.
As for the effects of adding the Apocalypse of Peter, I am not sure what they would be. We have only fragments of the text. The Church Fathers seem to have used it mostly it to establish that the children of adultery were still loved by God. Perhaps its inclusion might widely affect inheritance laws.
Edit: It occurs to me that we need to distinguish between Protestant and non-Protestant Bibles. Part of 2 Esdras (according to the current English numbering) is often called the (Jewish) Apocalypse of Esdras. So, this one is probably the most likely to be included ('added') to a Protestant Bible.