Never say never, there is alot of demand for sun destinations out of the South East and Waterford could be covered by a Aer Lingus Dublin aircraft on a "W" rotation.
But why would they do that? It would only damage the very successful sun routes they operate from Cork, and to a lesser extent Dublin. Aer Lingus aircraft can also land at Kerry which is a similiar distance from Cork as Waterford yet EI don't operate there either, presumably since it would only be affecting their Cork base. Even with a longer runway I'd only expect Waterford to have perhaps a Ryanair service to London and a few UK regionals together with a few charter flights to sun spots.