And we talk of Christ, we rejoice in Christ, we preach of Christ, we prophesy of Christ, and we write according to our prophecies, that our children may know to what source they may look for a remission of their sins. (2 Nephi 25:26). The "we" here is not an imperial we, at least, not in my opinion. Another word for prophesy is to testify or testimony (see Rev 19:10). If we take the passage as a parent talking to his children (in which case, that is what Nephi was doing), then certainly; anyone keeping a journal who testifies of Christ is writing scripture. Moses said he would that all the Lord's people were prophets (Num 11:29). And Paul said covet to prophesy (1 Cor 14:39). I think it is not beneath us to prophesy and if you write it then is it not scripture? So what is the difference between Canonical scripture and personal scripture? For the Old and New Testament, it was accepted by most of the Christian world by a conference of church leaders. What constitutes the Old and New Testament varies from one Christian church to another. But in the LDS church, for personal scripture to become Canonical, the entire church raises their hand in consent as proposed by church leaders in a general conference. I believe this was the case for the four standard works and every addition to the Doctrine and Covenants since it's inception.