Great Western Coffee Shop

One of the things that was mentioned in the recent Irish talks between the Northern Ireland and the Republic of Ireland.

Was a fast rail link between Belfast to Dublin 166kms (100 miles) and

Dublin and Cork 254kms(160m)

Its a good thought,

but to the best of my knowledge there is no passenger service tracks between Dublin Heuston and the main line stations in the east of the City.
 

Trains could run from Dublin Connelly through Drumcondra and pick up the main line out of Heuston to the west before Park West & Cherry Orchard - but it's a painfully slow link, only used (at the moment) by a few peak hour local trains.   It passes very close to "Platform 10" at what's described as Dublin Heuston but in reality is a separate station, and currently closed, just off to the side of the connector.

The Dublin - Belfast, Dublin - Cork (and Dublin - Waterford) services are ridiculously cheap compared to English equivalents. The problem is that they are infrequent (the Enterprise is 2-hourly), there aren't many services early-morning and late-evening, and at over 2 hours, they are a bit too long to be a comfortable commute (I've got no idea of the reliability). 

I'd imagine that the cost of providing extra services to make them more usable, plus some modest linespeed improvements would be relatively modest, though not quite as exciting as new HS rails.

Looking at the airplane schedule for the whole of Ireland,there are no scheduled flights Belfast-Dublin -Cork.

So if the airlines can't be bothered,why should the railway?

Belfast-Dublin on the train is much the same price as the coach, much the same journey time, but less frequent.