> Will there actually be a serious court case? ... In the case of repealing one of their prior rules, instead of making a rule, is there really a plausible litigable issue?

Yes - just like creating a regulation, repealing an existing regulation has to be based on a logical conclusion from factually demonstrable conditions. I found article https://www.nytimes.com/2017/11/22/opinion/courts-net-neutra... to be a good overview of this situation.