Also, rather than asia, I think it is Muslim countries that need a redoing.
Most of those are in asia though
Honestly while it would definately be nice with an expanded asian game I don't have confidence in paradox being able to carry out an expansion for asia (or perhaps even rotw in general?). The farther from europe you come the worse their research is. EU3s asia is pretty messed up, they've mixed up countries, dynasties and thrown in some fantasy countries for good meassure...
In general their research for rotw hasn't been the best in their games. They like making games about early modern europe after all and at this they are quite good. They've just given us an excellent expansion. While a new one for asia would be very nice I wouldn't count on it. Should they want to make another expansion I hope they would focus on the engine itself, give us a more detailed economy (just this would make for a huge expansion for asia in particular as the world economy to a very large degree was dependent on asia for all of the game's timeframe) and a better simulation of religions and cultures (in particular minority religion culture which would again make a huge difference in asia in general and in India in particular as the most of the states there where ruled by a cultural and religious, foreign minority). Enginewise Central Asia would also benefit greatly from a better way to simulate the nomadic tribes there.
Paradox has however provided us with a wonderfull engine and quite good research for europe and the areas immediately adjacent to it. It's entirely possible to mod the asian setup to greater accuracy with the current engine as the region isn't so different from europe as one might think. It is however quite different from how it's currently moddeled

but I doubt that means we'll see an expansion just for it (I would of course be very happy if one was announced though).