Here is the link recounting Dr. Gregory Popcak's personal experience decades ago in the Diocese of Pittsburgh (when he was a seminarian). The anecdotal evidence is that Rome has been approving the inclusion of women in the foot-washing rite for quite a while. So, why the great surprise when Pope Francis does it? Could it be that the media are just following the lead of certain traditionalist blogs to get a juicy story of alleged Catholic disarray? I do not think the mainstream media was sufficiently familiar with and aware of the issue to notice it at all until traditionalist blogs started venting.
By the way, Popcak describes outraged demonstrations by Catholics when the custom in Pittsburgh was changed to exclude women. Well, the existence of such outrage satisfies the canonical requirement that a custom that can acquire the force of law must be one that the community observes with the intention of introducing a law. Here is the commentary at pp. 90-91 of the New Commentary on the Code of Canon Law: "If the community is disturbed by and objects to the attempted removal, the intention to have a binding norm is proven." More recently, in the Diocese of Madison (Wisconsin), since the bishop does not allow priests to include women in the foot-washing rite, at least two priests (one a monsignor) chose not to hold the optional rite at all rather than exclude women (see link). That opposition--the monsignor was applauded by the congregation of the largest church in the diocese when he announced his decision--is more evidence for the existence of this factual custom under canon law.
Now turning to the Archdiocese of Baltimore, the nation's "premier episcopal see" and oldest diocese in the U.S., we see at this link a 2012 liturgical publication (go to p. 14) which allows the inclusion of women in the foot-washing rite and cites in support the 1987 statement so allowing from the U.S. Conference of Catholic Bishops (and reaffirmed in 2007 according to this Archdiocese of Baltimore Office of Worship publication).
The more I read the Code and the commentary to the Code, the more--in my mind at least--do the canonical objections raised against the Pope's actions collapse. Admittedly, reading Code and commentary is an acquired taste; but it is one that this controversy has given me to some degree.
Update: In the Archdiocese of Detroit, the custom of including women is alive and well. Below is a photo in the diocesan newspaper of a bishop washing the feet of a female on Holy Thursday, 2013 (see link). The other, older photo is from The Detroit News in 1992, and shows former Archbishop Maida (later made a Cardinal in 1994) washing the feet of a group including at least one female (see link). The last image is from 2007 and shows Bishop Boland of the Diocese of Savannah, Georgia (see link).