There are many skills and effects that are dependent on the distance
between two provinces (e.g. detect gates) or the adjacency of two
provinces (e.g. Civ level inheritance). This isn't the simple change
it appears to be at first glance. This is not to say that it shouldn't
even be considered but it's a big change. BTW there's a little ongoing
discussion regarding hex vs. grid maps on rec.games.pbm although no one
actually proposed changing Olympia's map to hexes over there...