As far as international flights - looking back at old Massport's Route Development plan http://www.maroundtable.com/aroundTable/1206/RouteDevPlan_GovPatrick.pdf it's pretty amazing how successful they were.
The only target still unfulfilled is Delhi/Mumbai and from the list of largest Boston markets not having direct flight the top one is Athens (although this doc is from 2012 so things might've changed somewhat)
The only target still unfulfilled is Delhi/Mumbai and from the list of largest Boston markets not having direct flight the top one is Athens (although this doc is from 2012 so things might've changed somewhat)