When Malta joined the EU it was suggested that they change to the right. They answered by stating that they prefered to drive in the shade.
Changing sides would mean a completely new bus fleet, and I suspect Ireland like the UK has spent a great deal of money already buying low floor buses which would be out of date if such a change were to come about. As for foreign visitors, when in Rome, do as the Romans do. I have seen many articulated lorries in Britain with a UK number plates over their country of origin plates, meaning they swapped the tractor unit at the port to suit the left hand drive. Sensible solution.