The main problem with fast roads is like Kobra mentioned, you can reach any town in 1 day even with the slowest scout heroes. If I remember correctly, the original setting for h3dm1 was fast roads, and then it was changed to average roads, for exactly this reason. If we want to experiment, I'd suggest playing slow roads.
I feel it's not a good idea to bring back fast roads, else it becomes week 1 rush-fest and endless scout fights.