There are many different creative tricks available to game developers to add spice into well-worn genres to keep them feeling fresh, but sometimes, it's the simplest and most-expected ideas that yield the most alluring fruit. Adding an entirely new clan or allowing an existing clan to take a dissimilar military/social path.
A renewed effort by CA could help to establish a more riveting experience both in combat and strategy with an introduction of new 'unknown' units quick thinking and adaptive strategy will again be needed.
It is not unreasonable for each clan to have had its own style, both in units and buildings. This would've been a welcome and necessary addition to Shogun2's ability to captivate and immerse.
The need to continually plot positions, adapt to new adversaries, that's where Total War ought be progressing towards, giving each clan, location, unit roster its own character and appearance.
As it stands simply the vision of something unseen before will be dazzling bullion to eyes whom have grown tired and soar from all the consistent standardized, indistinguishable sameness of units previously encountered.
Why not have variety in each clans: units, castles, fighting styles? At the very least some upper level unique units, like Empire made available towards the latter phases of gameplay. A units armour, appearance, configurations, castle appearance, configurations, make the faction what it is beyond the currently implemented 'variety' of Mon's and clan armour colour.