i have been thinking about this very same thing recently, and am quite surprised to find this thread here, and that there isn't something on the market with this service.

surely you would think with the power of ITA and google flights, to search prices for any destination, that the opposite should be easily available.

based in shanghai, and tickets are usually more expensive compared to other cities. would be useful if i can search for cheapest price to a certain destination from any city in china, and then just buy a cheap domestic ticket to connect from/to.