Skateboard/longboard would be a great portable method of transportation in a theoretical city with glass-smooth roads that have no cracks, potholes, or trash on them, with year-round temperate weather and little to no raining, low pedestrian traffic, rolled crubs, and mostly flat ground combined with gentle slopes. In every other scenario skating becomes just too injury prone. Even the largest wheels are like 80mm which isn't enough to clear junk and cracks reliably, ollie'ing up the curbs seems like a good idea but you can execute it perfectly 99 times and then flop on your ass the 100th, no matter how much practice you put into it because it's still a trick.
https://youtube.com/watch?v=M0KbEBgkVz0 
