I suppose the trouble with the Marshlink is that new third rail electrification, to my very limited knowledge, isn't particularly favoured. If it were electrified, I could see some government/ROSCO arrangement to donate the 171s for other use - up north, perhaps - and for that Southern would retain 3 or 4 Class 456s for the Marshlink.
I can see the logic for a two-car EMU working the line instead of a standard 377 or a 377/3 variant, mainly that some coaches would be carting around empty air from Hastings onward, and that they could be better used elsewhere. The absence of first class and the anger some people seem to have for any rolling stock over a decade old might nip any attempts in the bud though!
Perhaps if electrified, Southern could keep an hourly service to Brighton with the 171s or displaced 456s/377/3s. Southeastern could supplement the service, perhaps using a 466 from Ashford to Hastings only? This would bring the bay platform - Platform 1 for you fans of numbers - at Hastings into regular use by Southeastern, while keeping the through trains to Brighton operated by Southern.
Although there's no point improving a service if there's no demand for it.
I can see potential for customers wishing to make journeys from Kent to the coastway and vice-versa, customers wishing to make direct connections to London via HS1, and local commuters along the Marshlink. Certain events like Rye bonfire night and the weekly market see a slight increase in passengers. Perhaps advertising rail as a viable alternative to the car or other public transport might increase passenger numbers.
Ashford International to Tunbridge Wells using Southeastern classic is 54 minutes and costs £14.60. The same journey via Hastings takes 94 minutes and costs the same. I wonder whether there could be a market for journeys from Kent to stations along the Hastings line via the Marshlink at a slightly lower cost in exchange a longer journey time.
Hope my ramblings weren't utterly stupid and inane.
