I have formed Ireland a couple of times myself. Once a couple years ago, which was epic because you had to deal with mass-alliances with the 4 irish clans and tons of people guaranteeing them for no reason.
This latest patch though causes AI England to disband all their big ships and go mass carrack, which allows them to move in an epic army to come pwn you. This is bad for Ireland because they have a rough time handling anything above 8-stacks. They can hang around and let them attrition down for a little bit, but they have to build a high enough war-score from pwning stacks so they can get Meath in a peace treaty.
It's a long, grueling process. But possible.