What of local congregations and this day? Lutheran churches, especially of the Midwestern, conservative bent, will face the same sort of temptations that come along every time July 4th falls on a Sunday: patriotic jingoism and the the drafting of God Almighty into the service of the political aims of the United States. (Around July 4, a pastor in a nearby parish is famous for festooning the sanctuary in red, white, and blue and singing various patriotic songs.)
So I'm rather pleased to see that the Synod President has issued some very responsible suggestions. This is exactly the kind of leadership that a Church's chief pastor should give. If the suggestions are followed, the result will be a responsible ecclesiastical observance of a national tragedy that chiefly prays for peace, forgiveness, and healing and avoids politics.
As for me and my house, this day will be observed in much the same way we observe other national (and cultural - Mother's Day, Father's Day, etc.) days: the lectionary will not be displaced and the day will be acknowledged in some way in the sermon and in the prayers. But for those congregations which have their own reasons (chiefly geographical, I suppose) for a more profound observance, these resources demonstrate the proper flexibility of the Church's liturgy to encompass the pain, anger, and hatred of men and redirect it into the vein of godly prayer.