Following up on an initial posting here, I have some further thoughts on eucharistic presidency, beginning with some clarifications from the first, in response to some comments.
In some ways I can only state that not everything about being Anglican is 'scriptural' if, by that, one means that we do nothing without clear Scriptural warrant. It is part of historic Anglicanism that we did not accede to Puritan tendencies to become a bibliocratic church.
But this, we might observe, is not weird with respect to the Reformation! A recent read of a paper on Calvin's eucharistic theology, "Union and Communion: Calvin’s Theology of Word and Sacrament" by MICHAEL S. HORTON in International Journal of Systematic Theology Volume 11 Number 4 October 2009 (h/t to my friend Bryden Black), reminds me that no less a person than Calvin, seeking in his predictably intelligent and learned way to develop as error-free a theology of the eucharist as possible (i.e. avoiding some of the pitfalls that Luther and Zwingli fell into) found his way as much by digesting the subtleties of Eastern Orthodox eucharistic theology as by absorbing the participationist understanding of St Paul himself (1 Corinthians 10). In taking up the former subtleties, Calvin was very much in favour of the epiclesis - the calling of the Spirit - which is about as 'unscriptural' as one can get when reviewing important aspects of eucharistic theology and practice
Change in Anglicanism
When some moot change in Anglicanism, and others respond that change should be through consensus rather than unilateral action, a swift response often cites the case of the ordination of women, which was introduced to the Communion through unilateral action (although reasonably quickly received and accepted as a viable change even though not unanimously agreed with).
My argument re consensus being required for the introduction of lay presidency is that this is a more significant change to Anglican orders of ministry than the ordination of women (which, after all, did not introduce a new order of ministry) and arguably requires a greater degree of agreement than for the ordination of women. But I use the word 'arguably' advisedly: there is an argument to be had over whether any one province could decide for lay presidency and not cut itself off from Anglicanism.
A key issue
One of my correspondents to the first post raised the practical question which, across the Communion, must often arise: when a priest is not available to be president at a eucharistic service, why cannot another person such as a deacon or a lay leader be authorized to preside at communion until such time as a regular priest is available? One tension in modern Anglicanism is between the desire for weekly eucharist (rather than, say, weekly Morning Prayer and monthly or even irregular Holy Communion) and the supply of priests to fulfil the role of priest-in-charge or vicar of a parish (to say nothing of priests to preside at eucharists across a multi-centre parish). It certainly seems like a good idea to appoint non-priests to preside when priests are not available.
One response to such an idea is to make the point that presiding at the eucharist is a special task, in particular a special task of leadership. The eucharist is not a mere recitation of prayers in thankful remembrance of Jesus' death, followed by distribution of cup and bread. Rather, the eucharist is a gathering of the community of the faithful with the risen Christ in their midst, with the intention of feeding and drinking of Christ in accordance with his teaching and his commandment. Over this event which lies at the centre of the life of the church one ought to preside who is discerned and recognized as an appropriate leader to do so: eucharistic presidency is a special task of leadership (according to long and unbroken Christian tradition from the days of the apostles). This leadership is associated with episcopacy and eldership (bishops and presbyters or priests, in terms of church office set out in Scripture). On this line of thinking, a deacon or lay leader authorized to preside would logically be authorized to be a temporary presbyter.
In turn this would raise questions about whether (a) temporary presbyters are a good idea (they might be) and follow a concept known in Scripture (that, in my opinion, would be difficult to substantiate), (b) people can become presbyters on the basis of either authorization (without ordination) or ordination which has only temporary effect (either is possible, but neither, as far as I am aware, has precedent in the tradition of the Catholic, Orthodox, or Anglican churches).
Certainly it is true that Anglicans in different parts of the Communion have raised the question of lay presidency over several (or more) decades now. Various commissions have looked into it, reports written and recommendations made. The Diocese of Sydney seemingly has been within a hair's breadth of promulgating lay presidency for time beyond remembering. It may be an idea whose time will yet come.
But it is also true that it is the task of Anglican churches to discern priests, and the role of bishops to ordain priests and to appoint priests to communities of faith in order to ensure that eucharistic worship is conducted 'decently and in order'. A church working in this way is acting consonant with Scripture.