I flew Luton-Liverpool back in 2000 when easyJet was flying the route – it was the cheapest way of doing a day-trip to Manchester (leaving in the AM Peak, also counting the train option). That was before Liverpool South Parkway rail station had opened; still, having to take a bus shuttle is still more annoying than when the train directly serves the airport.
But back to the question, there’s a chance that BA might be up for more slot sitting – perhaps with a token daily service like the one they’re starting to Inverness. But I can’t see there being enough demand to justify a valuable Heathrow slot long-term – even KLM couldn’t make a Liverpool route work when Manchester provides excellent access to much of the same catchment.
For the foreseeable future, the most likely route will be a premium point-to-point, as VLM flew, into London City. but even that’s hard to see working given the far superior frequencies offered by rail and rather competitive journey times.
And yes, there’s been some talk about opening RAF Northolt to scheduled flights – but I think that would be hugely challenging to secure.
