If people use the SP to do some things interactively, then they are charged at the interactive rate. I don't think this is too much of an imposition other users or the machine. The real issue is whether one can control too tightly what people do on the machine. I think the answer is that one can't.
People make proposals to get work done, and allocations are made by a committee.
I would much rather see a broad array of useful software available for people to use as they see fit. The interactive charge factor could then be used as the mechanism that keeps interactive use reasonable if it appears to get out of hand. Its absence would be a major issue for us. I don't know. With thanks for your time.