This is a welcome, profoundly Anglican, document.
In Rowanese, it's pretty tough on the left side of The Empty Church. Rightly, he doesn't impose a solution, but frames the scope of the discussion to come. My favorite bit:
We do have a distinctive historic tradition a reformed commitment to the absolute priority of the Bible for deciding doctrine, a catholic loyalty to the sacraments and the threefold ministry of bishops, priests and deacons, and a habit of cultural sensitivity and intellectual flexibility that does not seek to close down unexpected questions too quickly.
Williams seems to be offering a challenge to what I'll call for the moment "Windsor Anglicans" in North America to form, or revive, such a historic Anglican Church, and to non-Windsor Anglicans to decide what they want in terms of Communion with the WWAC. If the Anglican Covenant goes forward (and does not make the mistake of being too narrow), the "Windsor" and "Non-Windsor" sides would have to decide what side they want to take, and whether they can abide by the limits set there.
Williams seems also to stick to a policy of making the Americans define themselves. It's as if his word to TEC is, "alright, you've decided you do not want full status. Do you want an associate status?" I think this is exactly the right note to sound.
Reactions will be fascinating to observe.