That would probably be insanely difficult to implement: would certainly require tinkering with the battle engine code. I like the idea, but then there are other issues as well: it will take an insanely long amount of time to play through one battle (though, honestly, I would fancy taking on such a map), and then there is the issue of enemy AI: with the very large battlefield, it will take a very long time for enemies to actually meet! The % of map covered in one step, even by the fastest units, will be ludirously slow.