I have heard of the preemption theory and you have nothing to lose except lots of money. You may never get pouchitis anyway.
It probably does not work in the vast majority of cases as treatment for active pouchitis. It does work for some people but it’s questionable whether those people are accurately described as chronic pouchitis patients. Some have one flare of pouchitis, get treated successfully with antibiotics then take probiotics and the pouchitis never recurs. To ascribe cause-effect in those situations is sheer speculation and not science. For truly antibiotic dependent pouchitis cases, most GIs have told me probiotics as an exclusive treatment for pouchitis is not likely to be effective. The probiotics are only as good as the formulation and amount and assuming that those strains will actually be a good target flora for the individual. Eating a lot of yogurt doesn’t hurt, and IMHO is just as likely to help.
I attempted cold turkey going off antibiotics and onto VSL3 multiple times, and each time I got substantially worse within a week. You run the risk of worsening the pouchitis by not treating it properly. Like Scott said it can creep up and slowly fester into something that constitutes major inflammation over time.