It was the Scottish and Republic of Ireland football associations which proposed the expansion of the European Championship agreed by UEFA member nations back in 2009, but it seems unlikely that both countries will qualify directly given they were drawn in Group D along with Germany, Poland and Georgia, as well as UEFA's newest member Gibraltar.
O'Neill said: "I think it's the toughest group but it's an exciting one. We have got Scotland, we have Poland who we have played in a recent friendly and whose recent efforts (against England) at Wembley were not too bad at all.
"Somebody told me (the associations had proposed expanding the tournament) so it is ironic they have ended up in the same group."
It will bring O'Neill face to face with his fellow ex-Celtic manager Gordon Strachan and he added: "They will be great occasions I hope.
"I'm sure he (Strachan) is looking forward to it. I'm sure he'll be as excited as I am myself. It's tough, there are other groups we might have preferred to be in but we'll get on with it.
"Germany you would say are the outstanding side in the group but there's plenty to fight for."
Scotland boss Strachan claimed it was a "terrific draw" - while other groups appeared "mundane".
Strachan said: "It will be tough for everyone involved in the group.
"Every tie has something in it. You've got Gibraltar, new to the competition; Germany, one of the best teams in the world.
"Then there is the Republic of Ireland and I think the two sets of supporters will turn those games into a cup tie.
"There are some groups you might call mundane but we're definitely in an exciting group. It's a terrific, terrific draw."
He added: "It's going to be very exciting for Gibraltar - I have been there a couple of times on holiday but I have never watched any football there, that's for sure. We will be looking forward to that one too."
Germany are the clear favourites to win the group but their head coach Joachim Low believes the fixtures against Scotland and the Republic will be tough.
Scotland held Germany to a 1-1 draw in Glasgow in a Euro 2004 qualifier in 2003, and lost narrowly in Dortmund 2-1 in the return fixture.
Low said: "We know the Scottish team will be physically strong and it has always been hard for Germany when we have played against them in the past.
"Gordon Strachan was a good tough player and his team will be the same.
"Martin O'Neill has been a top manager for a long time and his team will be a challenge too."
Scotland boss Strachan insisted that qualification was a realistic ambition.
He added: "If we play at the level we can play at we can definitely qualify.
"If we keep all our players fit we'll have a chance and the Republic, Poland and Georgia will be thinking the same.
"It's a hard group and I think any of the teams in our group will be saying this is going to be hard."
O'Neill said that the results between Ireland and Scotland could prove decisive in determining who qualifies for the final tournament in France.
He said: "The localisation has a big bearing on things and Scotland against the Republic of Ireland will be big games there, but it looks like a group where teams might take points off each other.
"That's the utopia really, to get there. It would be amazing if we could do it, but we've got a lot of fighting to do between now and then."
Scotland have the toughest of starts to qualifying, away against Germany on Sunday September 7, and the Republic of Ireland kick off their campaign on the same day away against Georgia.
The final qualifier will see Scotland play away against group minnows Gibraltar, with the Republic away against Poland.