EIR could easily fill an ATR-42 possibly daily. They have ran quite a few routes 4/5 weekly and that could definitely work, adding the US and Canada connections would be brilliant. From Cambridge to LHR or LGW can be awful in traffic and a cross city trek by train at great expense, DUB would be a winner. I agree BE could possibly make a go of it, especially with EI codeshare like at SEN.