The problem with building a realistic battle ship is that it would have to fire the entire distance of the map, and its shells explosions would have to be huge.
So it would have to have some sort of an artillery script build in it. (without the artillery you are stuck with a large PT boat, which many people have built)
But I think if someone could make a battleship, not nessecerily the Bismark, them it would be very popular. We've already seen huge aircraft carriers (the nimitz class) on OFP, now we just have to advance it. ;D