Something for me to put a pin in, and for perhaps someone else.
I suspect that most of the common, historic Unitarian, Universalist and Free Christian communion rites — those descended from King’s Chapel excepted, but including James Martineau’s — can be traced back to Frederick Henry Hedge’s translation of the Liturgy of St. James.
This would be a helpful hint in trying to improve those rites with integrity.
It would also be interesting to see when this liturgical influence was adopted, and when it was dropped. I think this task would be helped by the right bit of typography, to make the development more clear.