Overall, I think it is a positive development. It is a loud signal of two things. First, his desire to take a churchly approach to administering the LCMS. Second, it is the latest chapter in Fr. Harrison's obvious affinity with the early history of the LCMS (See: At Home in the House of My Fathers).
It is this second point that contains a potential negative aspect to this new part time job for the president. It was once common in the Missouri Synod to say that a "clergyperson without portfolio" (In Dr. Scaer's felicitous phrasing) was not really a clergyperson. That once you didn't have a call to a parish you were not rite vocatus, could not administer the Lord's Supper, ceased to be a minister.
This is nonsense and I have already been somewhat disappointed by analyses of this new part time time job that have called on AC XIV. Father Harrison received his call to serve the church in the process that culminated with his ordination and included his seminary education, examination, and election to the pastoral office.
Your ordination marks the end of the path of the church making you rite vocatus. Everything after that is detail work.
So let us congratulate both Fr. Harrison and the parish that will gain his not inconsiderable pastoral service on a part time basis. And let us hope this portends a churchly approach at the purple palace. But let's not return to that unfortunate theology that would insist that he wasn't rite vocatus this past Saturday.