Seattle would be on my wish list. While it is an ultra long haul flight distances are comparable to say
HKG-
JFK which
CX seems to pull off quite comfortably with current generation aircraft.
SQ's A350s should be able to do
SIN-
SEA nonstop. In
SEA they can always code share with
AS who seems open to working with various airlines and in view of their current relations with
DL would probably be open to code share with
SQ. This would open up various new city pairs for
SQ such as
SIN - San Jose/Boise etc which will be too thin to be served by
SQ but code share with say
AS may work with a non stop to
SIN. I have been to
SEA and it certainly seems pleasant enough to transit through.
Closer to home I reckon they may consider Phuket. Silkair will soon have 5 flights a day and further expansion on the route is limited for
MI which is surprisingly successful on the route despite LCC competition, due to capacity constraints at
HKT.
SQ could easily put in a wide body on this route during peak times to increase capacity.