I tend not to get involved with this kind of thing online, as it seems to be an incredibly divise topic for some and a very puzzling one for others, but a good starting point is A Brief History of Ireland by Paul F. State, which explains the Irish Romantic Movement of the late 1800s and the Gaelic League's search for a political/national identity in the very early 20th century. The leine (shirt) was suggested and quickly discarded as it was merely a shirt.

Patrick Pearse investigated the possibilities of an Irish national dress, looking at reviving a middle ages style costume for a Feis, which consisted of a long shirt with what appears to be hose or trews underneath.

Copies of Patrick Pearse's 1900 suggestions to reject the idea of this costume as being not fit for "an Irish gentleman", (the original Gaelic League were very snobbish, many of them were wealthy and/or aristocrats living in England but owning land in Ireland, much like the Highland Society of London were to Scotland). The full text is online here, (and copies exist on microfiche in London and even Sydney, Australia), but it contains the much quoted lines: "Frankly, I should much prefer to see you arrayed in a kilt, although it may be less authentic, than in a pair of these trews.

You would if you appeared in the latter, run the risk of leading the spectators to imagine that you had forgotten to don your trousers and had sallied forth in your drawers. This would be fatal to the dignity of the Feis.

If you adopt a costume, let it, at all events, have some elements of picturesqueness".

This seems to many to be the point where the decision was made to attempt to adopt the kilt as part of Irish identity. (Don't shoot the messenger, I have lived and worked in Ireland and I'm not just quoting from books here, it's a general perception of a failed idea. I also get fed up with folk calling the leine a proto kilt or a tunic. Leine means shirt, and it did so as far back as the 1500s when Irish troops are described by 3 different authors as wearing shirts that they call leine under their tunics. The kerne that fought for Henry VIII at Boulogne created a stir when they arrived because their "privvets" could be seen dangling under their leine. Leine that exist in Irish museums that I have seen with my own eyes are linen shirts, no more no less).

I suppose that the idea of a National kilt in Ireland was both a gimmick and to attract attention to a Nationalist cause, however, the idea was only initially taken up by "Gentlemen" such as Bernard FitzPatrick and Pierce O'Mahoney who wore the kilt while campaigning in London, and some of the afore mentioned very wealthy people who were born, raised and educated in England while owning land or title in Ireland, such as John Randolph Leslie, William Gibson, Baron Ashborne and one of the first , if not the first, Irish "warpipers" Louis Noble. Although these people are mentioned as wearing the kilt as a symbol of Irishness while in England, I have not found references to them wearing a kilt in Ireland. Certainly, whatever they wore, they did not sound like Irishmen, as Louis Noble later found out on two occasions when he was held at gunpoint by the IRA who assumed he was English, (which, by birth and education, he was).

Pearse taught in a fee paying boarding school where the kilt was briefly the school uniform. Irish bagpipers wore kilts, from possibly 1903 onwards. Certainly 1903 was the year that mouth blown bagpipes began to get mainstream exposure in Ireland as part of a new national identity, with
donations from the aforementioned very wealthy people, such as Lord Castletown who financed the large issue of bagpipes to Irish regiments that year. Scottish instructors and even a Scottish bagpipe firm were brought over to Ireland to ensure that tuition and instruments were of a high quality.

As the Gaelic League gained more members who were more inclined to direct action rather than poetry, music and clothes the leaning went toward the Irish Volunteers and the National dress idea dwindled. All in all, the adoption of the kilt it was not a success, to the majority of Irish born people it was not important. It is fair to say that the kilt has been worn in Ireland for over 100 years.