This island already has 9 operational airports with scheduled services and likelihood of another at Waterford reopening in the near future.
What we need is a strong hub with global connections, with the right infrastructure to support it, i.e. train system and adequate parking at a realistic price. While I'm all for DAA having competition at DUB for parking and even for terminal space (suggested T3), but opening a new rival airport in Arklow would significantly dent the DUB offering - if it is of any scale.
In any case I think it is unlikely to be approved.