I created a spreadsheet for similar purposes a few months ago using ExpertFlyer and all the intra-asia Cathay destinations in HK. The killer in the end is that most of the cheapest tickets now have a 5 day / 168 hour maximum stopover time, so nesting multiple cities becomes a lot less practical.

There were some good combinations already mentioned here, like ICN was pretty cheap for SIN. I seem to remember Philippines was the cheapest way to get to ICN etc. And it's expensive to do HKG-TPE, but was pretty cheap to do something like BKK-HKG-TPE.