What would a Unitarian drift Anglican Church look like?
Theologically it would be one that required no doctrinal promises or commitments of its clergy and lay leaders or such minimal promises (say to "faithfulness of the tradition") that interpretation could become highly diverse without a sufficient centre of gravity towards a trinitarian with Pauline salvation faith.
It may well be following Jesus but in a more rational and post Darwinian sense: that he is an off-centred human just like the rest of us when it comes to the chancy way of the universe. It would be interested in his ethics and context rather than some supernatural development in a tradition that delivers salvation by belief in Jesus as the Christ.
Early Unitarian belief, that Jesus was God's sole salvation authority figure by the will of God - a man given the power to do miracles and was resurrected by God - would be today splitting hairs. This belief in Unitarian days was related to Word, to the actions of the Spirit and to the fatherhood of God. These days we cannot tell this apart from Trinitarianism: these days Unitarian or even Arian beliefs are expressed often with the will to be trinitarian. But even if they are not, the expressions are too close, not (as they once were) too far apart.
Unitarian drift could still include the vastness of God and the working of the Spirit to bring the new from the old, but the Jesus as an indicator of the ethical nature of God would be just one example, not the core.
The Bible is something particular about something general. Once for the Karl Barths and near, the particular was what mattered, but a Unitarian drift is that the general matters and the particular is open to the full range of critical techniques in trying to understand what faith and trust means, and how to practice.
Liturgically a Unitarian drift would be a change towards frequent revision of liturgies rather than trying to fix with one over a long period (revision does not include correction according to fidelity to tradition), and would include clear theological change. Choices of liturgies would come in. There may be relaxation away insome cases from liturgies altogether (in England this seems to be something evangelicals and charismatics do, rather than liberals). Up to now litugical revision seems to be about changing language and about a different stress on Eucharists, as well as accuracy to ecumenical tradition.
No Anglican Church on either account seems to have a Unitarian drift. Of course there are revisionist theologies and people who half believe this and that and believe lots of other, and no doubt many could write different liturgies. But leaders give promises to the tradition and to using particular forms of worship. These promises would either have to end or become something understood in a different way (that the worship allowed was accepted as varied in content that a promise did not actually mean anything specific).
Remember this would be Unitarian drift: not Unitarian. Unitarians have readings that come from the Bible and other sources, and prayers that range from contemplations and meditations through to prayers to a listening being. Unitarians have services with Buddhist, Pagan, secular (say art or science) as well as Christian origin themes, and few services today follow a fixed liturgy or even choices (though some churches produce their own).
Now it would be expected that the non-drifting Christian Church has interfaith services where Christianity is represented in a fairly conserved way. Of course, if a church has many such services without invitations to representatives of other faiths, then it might be said that other things are going on - akin to a Unitarian drift (or Universalist drift, on a more modern understanding of Universalist). But the odd service in a community of different faiths is evidence of nothing.
A Church (denomination) with a Unitarian drift can still have bishops and the synodical structure. However, if those bishops were becoming understood as superintendents, and if a belief in apostolic succession was being dropped quietly, then this might indicate Unitarian drift (Unitarianism proper has two bishops), though probably with other theological and liturgical developments.
There are all sorts of laypeople, clergy and even bishops who have views compatible with the above, but they do not form a movement for change: even the Modern Churchpeople's Union might tolerate Unitarian views but does not promote such a drift.
The Church of England has done one thing in this direction only, and it is to relegate the Thirty-nine Articles to historic formularies. No clergyperson has to agree with them in any detail now. The rest remains intact. The rest remains intact in every Anglican Church, whatever the shades of opinion that do exist.
Now perhaps some people are a bit postmodern or novel-like about these beliefs. Incidentally, Unitarianism and postmodernism in some understandings have not got along well: Unitarianism was a project to preserve as much 'truth' in belief in an objective system as simple faith supported. Conscience and decisions about believing were subjective and individual. Postmodernism tries to overcome the objective-subjective divide, and postmodernism works best with more clutter not more simplicity. Unitarianism historically wants to know what is in the box, whereas postmodernism and Christianity is interested in the box.
Today much Unitarianism is 'playful', as good postmodernists often are, with its various belief elements. There is more in the way of collective packages and groupings, and less in the way of pure individualism. But Christian postmodernists hang on to the package: indeed some can be very conserving, like the Radical Orthodox. That they stick to the one means there is no Unitarian drift here: it is trying a new way to revitalise trinitarian Christianity when there is no objective truth about such a belief package - you just follow it. Such is not a drift.
So for Unitarian drift you need a really humanising Jesus according to how science understands the development of humanity, that the Christian Bible is but one view of something much wider, that the Pauline origin tradition gets replaced by a broader view of religion and salvation, or that there needs to be something like a frequent interfaith approach to ordinary church services. Liturgically there needs to be revision towards variety and simplicity and actual theological change involved.
This is not found at The Episcopal Church, or the Anglican Church of Canada, or at any other Anglican Church. It's not that it cannot happen: it can. It just isn't.