What is Trajectory Theology?
Trajectory theology or hermeneutic has to do with an interpretive method which finds progressive change in the application of Scripture through the trajectory of time going beyond the completion of the New Testament. For example, Robert Webb's book Women, Slaves, and Homosexuals proposes a trajectory hermeneutic on the issues of slaves and women, believing that while the Bible never completely overturned the the institution of slavery or the degraded role of women we should none the less look toward the direction in which the Scripture was headed and see a trajectory in time that plays out in our present understanding even though the NT had not made it to this point yet. In other words, whatever direction the Scriptures were heading, we are to take up that ball and carry it to its finality.
There are many difficulties with this hermeneutic:
1. What is the finality to which we are to take it?
2. How do we know that the NT example is not that finality?
3. Who has the authority to make these decisions?
This most basically is progressive revelation that does not find its interpretive completion at the close of the canon.
Bible.org does not have anything written on this that I know of. But there are many reviews of Webb's book. Look here for Look here for grudem's response: https://www.etsjets.org/files/JETS-PDFs/47/47-2/47-2-pp299-346_JETS.pdf