I've been looking at the timetables and looking at movements in and out of Limerick Station. Since I don't have access to anything inside IE I'm just going on the printed timetables.
arr ex LJ 0829
arr ex Sixmilebridge 0839
arr ex Nenagh 0842
dep to Ennis 0845
At present, the Nenagh service having split departs north at 0728 and south at 0740. Let's assume there's a reason why it has to wait for the northbound train to get half-way to Cloughjordan.
At present the line is timetabled for 24mins ex Castleconnell rather than 20 on the other two daily SBs so presumably there is a hold for four minutes to let the Sixmilebridge train into Colbert ahead of it, but a combination of that few minutes faster down from Nenagh on CWR and letting the train slipstream the LJ service... not sure how close in time they could operate between Killonan Junction and Ennis Junction but maybe 0836 is doable?
That extra six minutes might take a lot of pressure off someone with a 9am start given that most of the big offices are a decent walk from Colbert. If it worked, it might permit something completely crazy like using the Nenagh train for the 0845 departure to allow same-train Nenagh-Ennis journeys.
At present, the poor current track condition might not permit adequate reliability on those timings so perhaps IE have preferred to hold back until now - I seem to remember them changing the timetable not long after launch for that reason.