I was passing through the junction on Monday and an IR chap showed me where the new platform was going. He told me the reason was so that both the north and south going Cork main line trains could arrive and stop in the station at the same time allowing more flexible time tabling as well as less wait times for connections to Limerick, Ennis, Galway, etc. But they will have quite a bit a walk and climb instead of just across the current platform. I don't understand because Mallow has two platforms but they nearly always use the same one for both north and south bound trains so folks just have to walk across the platform to connect with the Killarney/Tralee trains.
Limerick junction is a shadow of its former self. Way of the world it seems there are just so few foot passengers on ferrys and intercity rail compared to decades ago. I was watching a programme on TV where an academic explained that before 1940 in Ireland urban planning and design focused on people movements by foot, cycling, and public transport (i.e. nobody had cars), but since the era of the car the focus shifted to roads hence the massive fall off in national rail transport except for urban commuters. Agri transport which used to be the country's biggest industry is now all by road, but 60/70 years ago it was nearly all by rail. At least with models we can go back in time to a golden era of railways.