Dream on . . .
What is needed is a development such as Weston (although planning may stop this) which serves the south and west of the city, including easy access from Kildare and Meath and the southern parts of the M50.
Dublin Airport is fast becoming inaccessible at other than off-peak times for many of us who live south of the river due to the congestion on the M50 (unless you leave a few hours travel time) - a useful measure would be the number of people from this region who would consider flying Dublin to Cork if it used Weston.
There is absolutely no need for a new airport to provide better access to the city centre - the 8km taxi journey from DUB once the Port Tunnel works finish will be as good as many "city" airports, plus if the visitors want to visit the IFSC and docklands, the taxi can spend a few extra quid to use the tunnel and shave ten minutes at least of the trip time.
Give Dublin Airport a speedy security process (giant leaps have been made in the last few months), speedy car park access (at non-extortion rates), direct metro link and speedy runway access and it would be perfect for city centre access.