Norse-Gael
Another culture that should probably already exist in 1066. The Norse-Gaels were fairly influential in the British Isles throughout the Medieval Period. Perhaps Norse Heritage but Goidelic language would be appropriate? I'm open to other combinations as well as I am not a big expert on Norse-Gael culture. I imagine the Isles, Mann, and perhaps a county in Ireland would be Norse-Gael in 1178.
English
This is a culture that already exists in the game, so I'd be surprised if they do not add it. Arguably, the King of England may still be French culture during this period. His vassals are a different story though. In CK2, English culture dynamically appeared starting in the year 1100.