Well if
VB want to go to Singapore and Hong Kong, they're going to need something bigger than the 737. A 767 or 757 would be ideal!
As for the -900, one of the problems being encountered is that it's still single aisle and with more pax than the 800 it obviously increases turnaround times with the unloading and loading of pax. If the 2nd fwd door was utilised it then hardly beats the 800 for capacity, and the 800 also has greater range anyway! Not the ideal aircraft for domestic ops when compared with the 800!