Far from starting to take over, railcars have long since taken over the remaining routes!
The majority of the Dublin-Cork runs are loco operated but some of the diagrams can be worked by ICRs, for example, and I'm open to correction, I think the 9:00 Heuston-Cork and its return working is an ICR turn. However the early morning services out of Cork/evening Heuston-Cork services should be a safe enough bet for loco operated mkIVs unless something goes awry.
The Dublin-Belfast Enterprise is your only other option for a loco operated service train, might be a bit out of your way though. As with the Corks these are 201 operated push-pull sets (Die Dietrich carriages rather than the CAF mkIVs). The RPSI is the only Irish TOC with conventional (non-push-pull) loco hauled stock these days, unless NIR ever choose to resurrect the Gatwick mkIIf set.
A pretty boring fleet from an enthusiast's POV but it has to be said it's a far more efficient system than it was 10 years ago.
However, if you can make it up to somewhere between Kildare and Portarlington on a weekday you should get some opportunities to photograph freight workings, there are liner and timber workings between Waterford and Ballina, along with the Dublin-Ballina IWT liners.
Actually, it seems likely that the 2700 railcars will be mothballed so if they're still in service by the time of your visit it might be worth getting a few shots; at the moment the majority work in the Limerick area, not sure if they'll still be there then though.
