The only airline in my view likely to fill the void on Dublin Bournemouth would be Aer Lingus Regional (RE). However, they are discontinuing MME and DSA for the winter so I cant see why they would now see BOU as any more attractive than either of those airports.
In terms of Flybe doing the route,, Ryanair and Flybe stay well out of each others way. Flybe have a savy formulaof reasonably high frequency on aircraft that are suited to many of these type of routes with low operating costs. For BE to operate this route they would need a W pattern or a new base. Neither in my view are likely.
Could bmibaby or Jet2 be attracted to the airport in the context of a Ryaniar withdrawl? WW have closed there Jersey route quickly enough but with Ryanair with such a big presence at their primary base at EMA would they look to BOU?
EI-BUD