In an ideal world, with money no object :-) I would like to see a rail link from a new platform at Parkway Station tunnelled to a new underground station below the terminal with escalator links to check-in.
It would need to have twin tracks or passing places, and vehicles would need to depart at frequent intervals, especially at peak times.
Tunnelling is very expensive, as would be the construction of an underground station, but in the long term such a solution would offer most capacity and most convenience for passengers.
Just to make my wish-list even more fanciful, I would like to see the link operated by the train company holding the Bedford-Brighton franchise so that frequencies can be mandated, through tickets sold, and connections made easy.
Time to wake up?