Problem with this is this is relatively unproven, heavy, expensive and more likely to break down.
Over any reasonable timeframe it is cheaper electrify and use a straight electric train.
We need a high performance 0-100kph in 35 seconds urban train, there is no way a DART with a few diesel engines under the floor can do that.
In the time it will take to order the trains, you would have electrified the Maynooth line, civil works reasonably quick, ordering and commissioning trains slow
This is classic government indecision, they won't authorize of the funding of the electrification but we know it has to happen and buying an urban diesel powered train right now is bad idea