I think the whole thing is extremely interesting, partly because we have far more questions than answers!
First, I believe that what we call Ceol Mor is extremely old, going back to Proto Indo European times.
That aside, Ceol Mor is theme-and-variation which is quite widespread in IE and other areas. I was talking to a traditional African harp player and that tradition has amazing similarities to Ceol Mor.
The tantalizing thing about Ceol Mor in Gaelic culture is though its vehicle for a thousand years (or several thousand) was the harp it only survives as a living tradition on the Highland pipes. Bagpipes as we know were a relative latecomer to the Gaelic fringe of Europe, the pipers evidently having to find ways of adapting Ceol Mor to their instrument.
Sadly we have very little to go on to imagine what Ceol Mor on the harp sounded like, because the harping tradition died out both in Ireland and Scotland. (We have to keep in mind that all modern Celtic harp playing is a revival, not a survival.)
I think echos of an Irish theme-and-variation approach to air playing still survives especially on the uilleann pipes. I’ve heard Paddy Keenan and other pipers play an air in a straightforward way (the ground) then in the first repeat add ornamental runs between certain notes, then on the third playing add even more elaborate runs.
I’ve read that this was especially done by Munster uilleann pipers, but that that tradition has died out. I just can’t remember now, a musicologist or music enthusiast wrote down some performances which hint at a partial survival of Ceol Mor.
O Neill’s Music Of Ireland has a number of airs showing this. Now one can say “those aren’t like Ceol Mor!” and true they’re not like the Ceol Mor which has come down to us through the Highland piping tradition. But this style of Irish air-playing might be just as close to what the ancient Gaelic harpers played as Piobaireachd is. Until we find a 900 year old recording of a Gaelic harper, who can say.
About that Wiki article, it talks about many modern musicians doing their “take” on what ancient Welsh, Irish, Harp, etc Ceol Mor sounded like. We just have to keep in mind that the evidence is slim and open to a wide range of interpretation.