I am planning a trip between two cities (City A and City B) and want to introduce a stopover of a few days in a third city (City X). I don't know which third city to go to, I want the search engine to give me all possible options where city X could be (eg, San Jose, San Francisco, etc.). To minimize travel friction, I want both legs of the journey to be strictly non-stop flights (i.e., non-stop from A to X, and non-stop from X to B).
Most flight search engines I looked at such as Google Flights and Skyscanner are optimized for single-ticket layovers or multi-city routes based on airline alliances. They don't easily allow you to reverse-engineer the intermediate destination by searching for the "intersection" of non-stop routes. E.g. , if using the multicity option on Google flights, one must specify at which airport the stopover occurs: instead I want the flight search engine to list all possible airports for my stopover.
How can I easily find all the possible intermediate cities for a stopover where both legs are strictly non-stop flights?
It'd be better if the system has a few features e.g. show prices. Arriving and departing the stopover from different airports serving the same metropolitan area would be another convenient option to have, in an ideal system one could specify the allowed radius (which could be expressed in metric distance, time to travel, etc.)
