A Munich link is a possibility, but it would probably be a seasonal Eurowings connection rather than LH or LH Cityline. I can't see FRA happening anytime soon due to the airport being slot restrained.
NCL is pretty well connected with Star Alliance: SAS to CPH and by proxy to BRU with BMI given that SN codeshares.
I honestly can't see NCL getting any other full service carriers in the near future. Ryanair, Eurowings and potentially Vueling will open up the majority of new routes over the next few years.