This news is being spun--on both the hard left and the hard right--as a setback to the initiative of the Communion Partners and the signers of the Anaheim Statement. It is, in fact, nothing of the sort. It's not even news, since this is precisely what the Archbishop told the seven CP bishops who visited him a month ago. Dr Williams is just stating the facts, as dull as they may be.
He is also being utterly consistent with his previous words and actions. (Rowan is nothing if not consistent.) In order for the covenant process to have any integrity, the document must first be offered to the provincial churches. I believe a good case can be made that the Episcopal Church has already materially rejected the covenant in advance of its promulgation by General Convention's adoption of B025 and C056; I have made that case myself. But it has obviously not yet done so formally, and it is on formalities that we must stand in situations such as this.
By rejecting the covenant, as I believe will happen in 2012, TEC will, per the Archbishop's consistent schema, be relegating itself to the second Track/Tier of Anglicanism--that is, "associate" status. It is only when that happens that the actions of dioceses such as Central Florida (with others to follow, I have no doubt) enter the game. There will then be a solid basis on which Rowan and the other Instruments of Communion to recognize "endorsement" as de facto "adoption," and maintain the fullest sacramental communion with endorsing dioceses (and, one hopes, parishes that are under the non-geographical oversight of bishops from endorsing dioceses). The Archbishop's letter to Bishop Howe pretty well says as much. You don't even have to dig between the lines; just moving a few leaves and twigs will suffice.
This letter is not a "development," and is nothing for anyone to stress over.