I know DUB-BRU is technically possible in an ATR-72, but would it really be practical.
It would be nearly 2 1/2 hours, hardly comfortable in an ATR-72.
It would seem a sure fire way to encourage expense account travelers to give Ryanair a go.
If they were to use an ATR 72 to BRU, it might make more sense from ORK, where the A320 seems too big for the route and Ryanair don't compete.