"Not so sure whether a short hop to Liverpool might work though"
Air Wales have just pulled this route after only six weeks.
However, I wonder whether it was as much to do with advertising (or lack of), timings, a route start-up in December and price, rather than a genuine lack of potential customers.
Newcastle-Bristol seems to work with easyJet, so you would think there is a market for the right product on Newcastle-Liverpool, admittedly a shorter distance but equally difficult by land transport.