While introducing Navan/Dublin commuter rail services via Drogheda is not the ideal option, a useful service could be established by investing a small fraction of what would be required to complete the line from Clonsilla.
The main requirement would be to upgrade the line to a sufficient standad to support up to 90 mph thus bringing the Navan to Drogheda jorney time down to 15 minutes or less. Navan trains could run limited stop beyond Drogeda, perhaps with a similar stopping pattern to the 0630 from Newry, but continuing to the Grand Canal Dock turnback. Journey time to Connolly of 55 to 65 minutes should be possible and would be sufficiently competive to attract business. Completion of the layout at Clongriffin would give some flexibility for faster trains to overtake the capacity hogging and slow moving DART trains.
This would be an interim measure to parially satisfy the demand for commuter rail services from Navan.