A simple requst that in CK2 all characters have two cultures, rather than just the one as in CK1. This would allow subtle cultural shifts to occur over time. For example in 1066 the nobles in England could start out as Franco-Norman, but over the generations of living in England can become Anglo-Norman.
This would also work well for nobles ruling over crusader states. Southern French conquerors may start out as Franco-Occitan, but further generations might form a Franco-Arab culture as they gradually adopt local customs.