"Concerns" are not necessarily actionable, but instead are problem statements that identify issues we would like to see solved/addressed by TrackBack.
From PhotoMatt, "A few of the problems with Trackback are immediately apparent:
Multiple Pings per web page. Outlawed? Permitted, but not advisable? Just fine?
TrackBack Ping ID guidance. There seems to be some confusion here and could use further clarification and refinement.