On the Island of Ireland, only the Dublin Area Rapid Transit (DART) and the Luas Dublin tram are electrified.
Iarnród Éireann has no major plans for electrification in the coming years. Through a mix of most services being intercity and only a handful of suburban services, it seems that there's not going to be much new.
There are currently proposals to extend the DART's 750V DC overhead wire to locations like Maynooth and to Drogheda in order to extend the network north and west. However, nothing has been set in stone yet.
The Irish Government, in a plan to modernise and improve the public transport options, has come up with the MetroLink. It is to be an underground, automated metro which will run through the city centre and will connect to Dublin Airport as well as further north to Swords. Not much in the way od details are known, but it's assumed to be a Standard Gauge line and will use either overhead wire or third rail. That much hasn't been made public yet.
Northern Ireland Railways, subject to UK law, is starting to consider their electrification options. Due to UK laws about the operation of diesel-only trains coming into effect around 2040, NIR has been looking into various options around electrification. Not much is known, but there has been consideration for something like a CAF CxK train type which will use overhead wire. It's assumed that it will use the UK standard of 25kV AC, but right now, this is all speculation. There's also speculation about bi-mode trains and some other things.
The only thing which is known, is that any replacement to the Enterprise service between Belfast and Dublin must be electric if it is to run faster. European Union regulations on diesel emissions will make a higher speed diesel train impossible to run, so electrification will be a necessity if higher speed services are to be done.