Yeah common guys! seriously! You can't sail across the ocean you will fall off the edge of the world! And you can't go to the moon it is impossible! Think Damnit!
The total war series shows that you could cobble the system together. But look at the compromises in the total war series. The tactical AI for the titles (Both medievals and Rome) I played was not challenging. I'm not sure you could create a challenging AI for a game that tactically plays out the battles. Humans are just a lot better at fighting than computers. The battles became a chore in the total war series pretty quickly because it was easy to win.
But forget simple gameplay issues. If you are talking integrating this with Mount and Blade, image how many battle maps you'd have to create. If you've played some of the mods for mount and blade (and they are excellent this is not a criticism of any of these games) you start to recognize the maps pretty quickly because making good maps in mount and blade is hard. Then you'd have to skin the units, make the weapons, and do all of this content development for all of the cultures. Then you'd have to overcome all of the technical challenges of getting a code base to work between a two dimension strategic layer and a three dimensional tactical layer.
All of this development cost would have to be completed on a budget for a game that would appeal to an audience that is interested in simming middle ages dynastic struggles (I love us but we aren't quite as big as the Madden football crew).
Finally you'd have to turn out a coherent product that focussed on what: tactical battles, dynastic expansion. I do software development for a living and hearing the careless uttering of, 'Oh, it should be easy' is something I hear way to often by well meaning people that simply have no clue how not easy what they are suggesting is. This would be hard to put together technically, from a game play standpoint and maintaining some kind of coherent product.