Part of the problem we had in getting things done perfectly was the lack of a strong Sempai/Kohai relationship in the Dojo. I see the relationship as one of responsibility and without a clear-cut set of relationships, some responsibilities for managing certain things for the visit and demo fell between the cracks and Kiyoshi Payne and I had to fill in those cracks ourselves.
When it comes to a situation such as the visit of a high-ranked dignitary to the Dojo, no mistakes can be allowed. In those cases, the Sempai/Kohai relationship becomes critical for ensuring messages are passed on, responsibilities assigned, and checks are done to ensure things are ship-shape. The Sempai/Kohai relationship helps by providing a structure for getting things done.
Well, here in Hiroshima, we have managed visits from high-ranking visitors with no problems and we do not have a clear cut sempai/kohai system in place. I think you can put in place an efficient framework for running the dojo without such a system.
Of course, our Japanese students might informally regard themselves as sempai or kohai, but I myself doubt it. The atmosphere of our dojo is quite different from that of the aikido club in Hiroshima University's Taiikukai, where sempai expect to be addressed as such. I suspect that the dead weight of Taiikukai tradition has an effect in maintaining the system--and in putting off increasing numbers of students from joining the club. So some of these students come to us, where they can have good training, but without all the sempai/kohai baggage that comes with it.