Does the PPT have enough headroom for electrification? From this image it would not appear so.
If it were possible to electrify the PPT, then possibly combined with a major re-organisation of Connolly it might be possible to have it operate as an interconnector. Given the amount of yard space in Connolly, would it not be a relatively simple matter to add a couple of platforms that could be dedicated towards terminating northern or Maynooth line services? This would enable DART frequency to be increased to the point where people wouldn't mind changing trains.
By relatively simple I mean relative to the expense of digging out a tunnel right through the city centre.