Apparently Bus Eireann launched an express frmo Dublin to Ikea. DOes anybody know if this is still running? Bus Eireann web site served only to exhaust and demoralise!
I had the same experience as you so I emailed Bus Eireann and they said the direct Ikea bus has been discontinued. They do run a bus to Belfast city every hour for €22 return, and you can get a local Belfast bus to Ikea from there. It's not as direct but it is a more flexible solution.
However if you search for "Belfast" on the Bus Eireann website it will come up with zero results. Apparently this is because you can't buy any cross-border tickets from the Bus Eireann website (Bit of a flaw in the system if you ask me). Apparently you just have to buy them in person on the day (not that the website tells you that, I had to email them again).
In the end I just took the train, and there is a bus stop just across the road from the station in Belfast for the bus to Ikea, about 20 mins. Couldn't carry the kitchen home, of course, but got my reconnaissance done.