If SEN DUB does not work, there is little hope for any non sunshine routes, especially given that Dublin/London is among the most dense routes in Europe if not the busiest.
That said service to southeast coast of England from Ireland have been marginal. Norwich, Manston, Southend or even Humberside...
The other angle may be that the SEN DUB routes is only marginally profitable and with scarce resource in terms or airframes they may have choose to open a range of European routes instead of having 1 route to Dublin.
LCY DUB is seeing serious growth as a result of BA Cityflyer and Cityjet competing heavily, this may further deter the route coming back...