Ehh.. I kind of disagree solely based of personal experience. I know a lot of people don't ride Simpsons because of motion sickness, including me. I've actually never been on Simpsons because of the stories I've heard of people getting sick (and I don't even get motion sick that much, FJ never gets me sick).
BUT..
I am ALWAYS in Springfield anytime I'm at Universal. It's one of my favorite areas of either park. I always sit down with a Duff along the water a few times per trip. It's also my favorite HHN S&S area for that same reason. If they were to build a new ride, I don't think capacity would be as much of an issue as it seems. I do believe the potential of added capacity from a high-capacity dark ride would greatly outweigh the detriment of it going down for a year or two.
Agreed based on what I said ^ there