It is these little things that BL is missing so much. GTA and Skyrim are filled with things that seem like they do nothing but really add to the lived in feel of their worlds and drinking is such a small easy one to do.This is another feature from WB that the devs could really improve and expand on. Make feasts actually matter. Have custom scenes and animations of lords around a long candle lit table, eating and laughing and talking. Introduce new interesting quests that can only happen at feats. Perhaps they could be based around political intrigue: Slip poison into Lord X's wine, Seduce the daughter of Lord Y, Get the King drunk and get some information out of him, Follow Lord Z to his secret lovers place and black mail him. Rewards could range from influence to gold to relations. Just give the player something to do for **** sake.
Or simply add the ability to get really drunk and let you walk around town or the keep in a drunk state. Something like what GTA does. It may seem trivial or useless but things like this allow the player to connect more closely with his avatar in game. It lets you care more about what goes on in this game world. Perhaps a particularly happy go lucky lord is always taking you out drinking during feasts and you form a soft spot for him. If he's ever killed in battle or executed it would mean more to the player than just text scrolling on the side.
I actually really want them to add to the friends and enemies mechanics that you touched on here with the drinking. Could they maybe make it so if you are good friends with a vassal they will maybe act quick to defend one of your villages or maybe your enemies go out of their way to target your villages or your caravans on the map. These are small things that would really add to the experience and make the world feel alive.