Too be fair, EI have not really been terribly successful in the past, when in direct competition with other airlines, from Belfast. Even when entering new markets, again, unfortunately not very successful.
We shall wait and see in this instance. Can anyone confirm if EI have codeshare or interlining agreements on their LGW. BE still appear to have BA codeshare, and Virgin Holidays seem to put a lot of business their way, so not relying solely on point to point...
EI may get people to switch and try their service, as the advertising pays off, but that gives no guarantee those people will then stay loyal to EI. Many will look to price and frequency ultimately...