wow i think you r fascinated by the shogun era ... like me
have you read the art of war ? watched movies ? made research about the samurai ? i did ..
it would be great to have shogun 2 .. personally i would like 54 turns per year .. but wit limited recruitment possibility .. say depending on the samurai in your region and your koku .. this would mean you would have to fight 10 15 battles to control a region ... a more realistic approach .. and it would mean loosing 500 of your 1000 samurai in the army would be a hard blow as you could not immediately replace them ... and the warlord leading the clan would have to make sometimes difficult desicions, as when to engage and how much is he willing to risk to take what is his neighbors ... many more "stupid" ideas pop up in my head :P
Of course i realize this is not for everyone .. as this kind if playing would take months to finish a game ... but it would represent the 150 years of the country at war as a huge struggle for dominance ... say you start the classical way in 1530 and end the game in 1615 - a total of 4590 turns - this would be still weary difficult as you would have all the 160 clans (if i remember correctly there were aprox 160), meaning 159 rivals .. of course as in real life you could make alliances, protect a weaker clan and finally absorb them in to yours ... as Tokugawa made whit the remnants of the Imagawa ( did you know Tokugawa was a hostage of Imagawa ? ).
This way adding all medium and large settlement and castles/forts in medieval japan you would sweat blood to gain dominance. An in a single year (54 turns) a clan led by a fool would disappear ... this way a year would mean making assessment how much you spend in 54 turns as you only get koku once or twice a year from harvest. And dont forget the japanese did advance in warfare as the used better made armor, had seen the power of the teppo ( oda made good use of it ) and there were even religious changes ...

can write pages on this topic .. but i think it would not have a huge success on the market .. as in our tome players r not really interested in deep playing stile games .. i guess i can dream right ?
Today games r made for 1 thing ... profit