Just like with regular bikes, you can add electric assist to them to extend their range and make the job of the rider easier. In this clip (https://www.youtube.com/watch?v=OCo4cRQMBlo) the rider gets an average speed on 37.5 km/h (top speed 84 km/h) over a distance of 73 km with over half the battery remaining. And that is without wearing the racing hoodie which significantly reduces drag.
The main problem with velomobiles is that they are expensive. The frame is made from carbon fiber and needs to be handcrafted. So the price ranges from about €5000 - €10000 which is too expensive to most. If some Chinese giant or billionaire investor set out to mass produce velomobiles I'm sure they could totally revolutionize transportation.