I actually agree that the interfaces are a good idea, and maybe something VSL will do in the future? I'm not good at registrations at all myself. That is one of the more difficult and important things an organist has to master if he is going to become a good player and I certainly never did. However, with all the pipes available on the Vienna Konzerthaus, it is possible to do some homework, studying the usual or unusual registrations, and then put them right there pipe by pipe into the VI setup. AFter the intial setup you can then switch instantly between instruments.
One thing that is really significant about the Vienna Konzerthaus organ is that you can have any other orchestral instrument play with it, in the space, by using MIR which is actually sampled in the same hall. That is a huge advantage since none of the other organs out there have a similar situation.