Not sure how late you are planning to go but might be cool to include the Normans as a non-playable emergin faction later on as they had a pretty epic impact for the short time they were around.
Would be a game event sorta "...a Danish Lord Rollo or Rolfgr arrives in Northern France, the French, fearful of their new rivals call them the Northmen or Normans..." The Norman army would aim to take the province that would historically become Normandy. If you happens to be playing as the Franks (or whoever) you will have the chance to change history and kick them out or if you are anyone else just sit back and watch them take Normandy, Maine, Brittany and perhaps Enlgand.
It might be an idea that if you are playing any Danish nation, that the Normans do not emerge as it is up to you where you raid etc...