Given that's he's played for Ireland all his career, the natural step would have been to do what his Ulster rugby counterparts do and represent the 32 counties union under which they fall, while maintaining a sense of Northern Irishness. I'm aware the option isn't open to Ulster to play for a United Kingdom side at international level.
Don't some of the IFA fans refer to players as 'bigots' when they opt to play for Ireland and that they are merely further pronouncing the division in the North? Well, it would have been pretty bigoted, in this context, if McIlroy had lined out for the United Kingdom.
Barnes makes one point in his tweets that I have a sort of agreement with. It would be nice to have one out-and-out Irishman in the pair- Shane Lowry or Padraig Harrington. McDowell and McIlroy aren't exactly tricolour-hugging Irishmen, if you pardon any 'bigotry' that may infer.