Reasons why it would be great:
-Better perfomance
-Modding tools
-Steam workshop, tough not sure if this is useful
-Better graphics WITH better perfomance
-Fall of Samurai has breech loading animations, gatling guns, Victorian era naval battles...
-Uses same engine, so i think it would be relatively easy to port everything you have already done to Shogun 2
-More stuff in campaign, such as upgradable Generals
-better AI
-You can toggle button to choose rank firing mode, you can choose kneel fire, and default firing mode could be "mass fire", so we have 3 firing modes choosable in middle of battle!
-Soldiers don`t shoot if ally is standing in front of you, but still there is friendly fire (cross fire, artillery etc.)
-Battle map editor
So if breaktrough in modding campaign map happens (long time ago i saw picture with modded campaign map in Shogun 2, it was bugged, clumsy, weird etc., but it was breaktrough, it was modded campaign map! So it definetly is possible, but still in baby steps), i see no reason not to port this mod.
EDIT: Oh, and Shogun 2 has sguare formation and bayonet animations, they just are same as in Napoleon TW so that is why they are not used in Vanilla