In terms of what I'd like NG to make,
I think Norwegian is an airline that often gets overlooked in 1/400. The only 737-800s that have been made are by Aeroclassics so it'd be nice to see them.
I'd also like to see more Thomas Cook and sas. Sas a321 old colours would sell very well in Europe as they fly to all major hubs. Thomas Cook was an icon in Britain and they still hold a great deal of nostalgia so they could sell very well in the UK.
I'm hoping for the day that NG develop a good a320 mould. Alot of people will grown at the idea of another a320 but honestly, I think its one of the most well known aircraft that needs a new mould.