1. Mid-game total war when the player makes a move towards Chang'An or the child emperor.
I get this idea when watching the 3rd Yuanshao stream, when Wheels move Lv Bu to Chang'An, Gongsun Zan broke vassalage and all his supporter's join his war against the player. It really tensed up things a little bit and made the otherwise peaceful campaign more interesting. I kind of hope it was because he made a move for Chang'An and emperor though I didn't think it was the reason. If that was actually the case then somebody pls tell me so I can rest in peace;)
I am making this suggestion because I think for total war game the early campaign is always the hardest part when your generals and units are weak, and your economy is bad and you have vulnerable frontiers all around you, but when mid game comes when you finally have leveled-up generals, decent units, and solidified cities, you have few challenges and just waiting for the late game events, I have countless abandoned saves from various factions in mid game, and tw usually couldn't offer a good late game experience. Partly because you grow too fat, Strong I mean, in mid game. I know the current 3 kingdoms and coalition mechanism sounds nice enough for late-game, but how about boosting up the mid-game challenge as well. And by making it tie to the capture of Han empire the player can control the pace! So if somehow in mid-game the AIs around you were giving you enough challenge then you could deal with that and do not move towards the child emperor. If not, you can go for the emperor while getting a nice prize but risk going to war with several Han loyalists or lords who are thinking the same thing.
I also think it would be realistic and easy to implement. Just giving a one-time negative diplomatic impact on some Han-loyalist factions will do, and based on your previous relations, at least some of them may declare war on the player so you would have an eventful mid-game.
2. Making some mission and guiding the Als to a more historical territory.
I know some would not agree with it, apparently tw is a sandbox game where you can make your own history and all. I am just bringing this up again because I saw a while ago in MaTeng's historical mod let's play that LiuBei's ShuHan was in the south of China while it was actually called Shu because his kingdom was located in Shu and that was in the southwest, and it makes sense for Liubei to retreat to the southwest since it would be hard for him to stay in central China with his limited army and economy at his start. I will not stress the point though for reasons above.
3. Please make Meng Huo an early DLC faction:)
I had this idea as soon as I did not see him in the launch roster, which makes sense I guess since he is not a big historical figure, but he and his tribe did play a big role in the romance. The more inviting reason will be you would not only get 'babarian' tribe warriors, special units, as well as war elephants, which was always a pleasure to see in a tw battle, and LiuBei would have more reason to go for the southwest when played by the player. Because at least for me part the fun of playing a Three Kingdom game would be to get all the heroes/characters I like in my faction.
I think I am forgetting sth but that's fine. It's not like they would come true just because I mention them right;)