No chance - too big and far too fuel thirsty. If you believe Ryanair they want A330 - smaller and fuel efficient across the Atlantic. There is no way that Ryanair would saddle themselves with both the costs of a 747 and the number of seats to sell. The A330 would be right, but I can't see them doing this as it is a mug's game to compete long haul on costs with the legacy carriers. You usually need to have a defining product to succeed long haul against legacy carriers (e.g. quality - Qatar Airways or accessibility - Emirates). Cost alone does not do it long haul in the way that it does short haul.