As an engineer licensed in 21 states: Its about time...man does it take an effort to market yourself across state lines. Keeping up with each states different requirements for licensure, continuing education, corporate certification, and ethics takes a great deal of time away from projects.
Now I'm normally a state's rights kind of person but I could envision the states saving money (most have bad budget situations right now) and creating a national licensure that would be sensitive to individual state's circumstances (i.e. California seismic). Develop a national license but allow the states to set limited requirements/levels for practice in their domain.