The problem with VLM expanding to other UK points is that the Fokker 50 is weight restricted out of London City and even on a 1 hour flight the airline will only book 47 passengers. Should weather conditions allow the airline may take extra passengers on a standby basis.
The airline would probably require Avro RJ's in order to operate flights longer than an hour.
Before anyone says that the Isle of Man flight is longer than an hour it is never full, no where near!