whatever happens you will either end up lagging behind a DART most of the way or you leave huge time gaps on the DART line effecting their passengers, inconviniencing a larger number to a cater for a much smaller number.
The Sligo line is an example of this. There is normally a (at least) 20 minute gap (peak time 4.40 to 5.15 is 35 minute gap- astonishing for peak hour!) between the last maynooth train to leave and the next sligo intercity. This is also considering that the Dublin-Bray stretch is longer than the Dublin-maynooth stretch.