Here's a what-if layout scenario, based on things which might have happened - or indeed, were actively planne at one stage.
It's 1965-70, and steam as not been consigned to the bin. CIE has under it's ownership the following:
A large fleet of D class, as they were considered perfectly adequate.
A reasonable fleet of modernised J15s on secondary or shunting duties.
A fleet of fast modern 2.4.4.T locos for suburban and branch traffic
Five 800 class on the Cork line along with twin-engined Sulzer diesels and inherited ex-GNR diesels of American and German origins.
Ex GNR 4.6.0 steam locomotives on the Enterprise
A fleet of B113 types....
On the DSER and Waterford lines, ex-GSR 850 class 4.6.2T locomotives; these, along with the 2.4.4T types, and possibly a modern mixed traffic 2.6.0, being a standard "modern" GSR / CIE set of classes, the last of which would be destined to remain in traffic until about 1990....