In regard to EI route. There was about a 50% increase in passengers transferring onto US flights from Europe and the UK through Dublin last summer. So they may be some hope if passengers do fly to the US. I would expect the route to be reduced to 2 daily next winter if it's still around. It was only a matter of time before Ryanair went back to 3 daily.
Both airlines seem to be able to cohabit routes into other airports, although I'm not sure Bristol and it's catchment area can support 789 daily seats*. The advanced base fares on both airlines are very similar, although of course Ryanair seem to do the cheaper deals a few months out.
Does anyone know if Aer Lingus do connections (ie. European destinations) other than on USA routes via Dublin? The website doesn't seem to prohibit through tickets, for example if I wanted to fly Bristol-Dublin-Madrid-Dublin-Bristol.
*Based on 3x 189 seat 737s and 3x 74 seat ATR 72s on this summer's weekday schedule.