This is a suggestion for a fun map. Players start off on the base map and as soon as the leading player reaches midway to winning (say, 5 out of 10 points to win), the map randomizes. The roads, houses, cities built remain constant, but maybe the numbers or the resources randomly change. Would be fun to see how the game progresses from then.
Or the trigger for the random change could be in the dev cards. As soon as someone randomly draws the card, the tiles randomize. But in this case, the game can finish off before the randomization occurs.