Let's grant you, for the time being, the notion that "Irish nationalism" aspires to dominate the world.
Nobody really "dominates" the world today. The world is actually carved into imperialist blocs, each with their own desires for domination. Irish nationalism cannot dominate the world, neither can it change anything since a new Irish nation state just would get integrated into the world market and would become part of one or the other imperialist camp as in Angola, where the MPLA bourgeois faction fought against the UNITA and the FNLA bourgeois factions in the Angolan Civil War. The MPLA were supported by the "socialist" U.S.S.R., the FNLA and UNITA, by "socialist" China, the U.S.A and others. All that came out of it was another bourgeois state, integrated into the world market. In the time of the U.S.S.R., Irish nationalists could perhaps have conceivably looked to the Russians for help and have gotten a national liberation (which may or may not have actually happened in reality). However, now that the U.S.S.R. no longer exists, a united Irish state would have to look for some other bloc, perhaps a future one formed by Russia or Venezuela(?), to come into existence, integrate into and survive. Either way, the whole exercise would be meaningless since the workers of all the countries in this hypothetical bloc would be already too infused with nationalism, subject to brutal international warfare and far too weakened because of their collaborating with the nationalist bourgeoisie to conceive of a socialist revolution. This was the pattern across all the anti-colonial, nationalist revolts of the past century supported by either the U.S.S.R. or China or India or some other power.