I'm not convinced that pouches (or colons) have a service life measured in numbers of bowel movements. Certainly the ileum isn't perfectly designed for the storage of stool or absorption of water, though it does get more colon-like in J-pouchers. Most folks with J-pouches do just fine; some of the problems are structural, when a pouch isn't built optimally, and some may be due to stool sitting around in the "wrong" place. We'll probably find out in the future that an out-of-balance microbiome is a big part of what causes some problems, but that's still a bit of a medical mystery.