Just supposing for a moment that Flybe could make some sort of agreement with Virgin Trains where passengers could buy a through ticket from Waterford to London which included a Virgin West Coast ticket to London Euston, that might make a daily - perhaps even twice daily WAT/BHX service viable, selling BHX as the gateway to London.
Far fetched? Well possibly yes given the totally un-joined-up nature of the UK's public transport system, but Swiss do it perfectly well with SBB - and Lufthansa with the DB. Any anyway, the transfer from BHX to Birmingham International station is quick, free and painless, and the Virgin service to Euston frequent and quick.