To begin, it's noteworthy that Wicks references the Anglican Communion as a "church" in the introduction rather than simply an "ecclesial community" (p. 6). He goes on to say of the ecumenical task:
The great gain afforded by the ecclesiology of communio becomes apparent when we ask what is the goal of Christian ecumenical efforts. Ecumenists are not striving for the eventual transfer of masses of Christians to some system of doctrine, worship, and church polity other than their own. The goal, rather, is the extension of bonds of communio between these churches now existing as separated communities of faith and worship.I think it's also worth noting the way that Wicks discusses "belief/doctrine, worship, and polity" here. On the one hand, he says in the first quoted paragraph that there does not need to be any shift to a new form of doctrine, worship, or polity for the churches. On the other, he says in the second quoted paragraph that ecclesial recognition involves an assessment of belief, worship, and polity as "genuinely Christian".
[...] The commitment to ecumenism means striving toward the day on which churches can turn toward each other and in the light of faith perform a mutual and corporate act of ecclesial recognition. This is the Christian unity we seek: churches acknowledging each other as valid articulations of what it means to be the church of Jesus Christ. Then the bond of communio can be extended between the bodies which have recognized in each other a total complex of genuinely Christian belief, worship, and polity. With full communio established, no further assimilation or organizational merger need be sought. (p. 6-7)
I've found this to be the difficult balance in ecumenical considerations. To turn back to my own work, my 2008 article on the Church of Nigeria and the Anglican Communion offers a much more restrictive and exclusivist approach to church unity... lines in the sand are drawn and certain beliefs/worship/polity are recognized as unacceptable. This presents clear difficulties for an ecclesial situation where one's fellowship with Christ through baptism and eucharist would supposedly be adequate for unity. On the other hand, my 2009 article on Protestant and Roman Catholic relations went quite far in an inclusivist direction... the work of the Spirit is adequate to establish unity, and to cite reasons of polity against recognition of the Protestant churches as veritable churches is to inappropriately pit one work of the Spirit against another. In this case, though, how does one decide where to draw the line determining belief, worship, and polity as "genuinely Christian"? And in the case of my 2008 article on the Anglican Communion, when does drawing a line become the sort of insistence on a "transfer of masses of Christians to some system of doctrine, worship, and polity other than their own" that Wicks denies as the goal of ecumenism?
Clearly both tasks are needed, so a judgment of legitimacy in one case and a recognition of what Walter Kasper calls "pluriformity" in another case doesn't need to be hypocritical or contradictory. But disagreement over discernment between the two in any particular situation is, I take it, the main source of disputes in ecumenical dialogue.