IAH-SYD: I doubt they can get enough to fill the loads for this flight. I live in Australia and I can honestly tell you that no one here has any desire to go to Houston. Granted, Australians will make up a minority of passengers (they tend to fly QF), but that minority does help make things profitable. SFO and LAX are great points for the SYD flights. An interesting one would be ORD-SYD, but it's pushing it distance-wise. Could be done though.
EWR-BKK: This would almost rival EWR-SIN as the longest commercial flight (probably be 30 minutes or so shorter than EWR-SIN). EWR-SIN is a Singapore Airline flight and it is Business-Class only!! (there are no E seats). I think some people might fly this one if it was offered, but not sure about 7 days/week departures.