In Germany, I noticed that a lot of the regional trains are made up of carriages hauled by electric locomotives. Would this not be a reasonable approach for Irish Rail to adopt? It seems to me that the current focus on DMUs for everything ignores the fact that that you're effectively tying the network into diesel over a 30-40 year lifespan unless you throw everything away and start again. I'm guessing that this approach only works for regional and intercity use.
Irish Rail do have history in multi-annual programmes to reduce costs. Look at the steady progress in removing manually operated level crossings over the last 10 years or so. You eventually get to a point where the operational savings fund the remains of the programme. Unfortunately this doesn't work if you're throwing away rolling stock with 20 years of life left.
In any case when you combine the implications of retiring perfectly good trains early and the fact that we're still burning massive amounts for coal and peat for power generation, the CO2 savings of electrification are marginal at best. You'd probably get better overall CO2 savings by investing in boring stuff like multi-mode integration, capacity, new lines (both light and heavy rail) and shorter journey times since you'd be taking more cars off the road by providing a more attractive alternative.