I too have felt the limitation in predictive power of Christensen’s work. Despite Lepore’s arguments (and Christensen’s rebuttal) and the limitations you have pointed out, I found that the concept is effective in ‘lighting a fire’ among executives. I discuss his work in EMBA and executive education lectures. Executive audiences find parallels in their industry and can often visualize what might be coming in the future and what they need to do to prepare for it.
Your question on what is ripe for disruption is a good one. I have usually framed that question as “What are the triggers of disruption?” I think whenever consumers experience ‘pain’ or are inconvenienced — due to extra steps in a process, make mistakes or errors, confusion due to incomplete information, or information overload, the process is ripe for disruption. When processes are germane to a the conduct of a business or a transaction, it can give rise to a Disruptive business model.
Whenever one finds oneself saying “there’s got to be a better way of doing this” or “if I were in charge, I would do…” serve as triggers for disruptive ideas. Of course, new technology can force disruption by automating a process and lowering transaction costs even when the consumer does not feel the pain. As do consumer preferences and deregulation as you pointed out.