It could be nice.

Somehow I can't imagine fleet system similar to RTW or M2TW in Shogun, though.

Japan should give us quite a few nice chokepoints, which means that the AI would have to improve immensely if RTW/M2TW style system is used (which sounds quite likely).

I don't mind gunpowder.

Diplomacy with the Western countries might add a flavor, but somehow can't see that playing a real part.

One thing I don't miss are the huge bonuses generals would give on the battlefield.