Interesting that cycling 24h record 900km is less than 2x of skateboard record 313m/503km. From my amateur experience with both, would expect cycling to be 5x-10x of skateboarding.
https://24hourultraskate.com/#records
The cyclist in this case averaged 37.5 km/h, which is really impressive over 24 hours. 5-10x slower would be 3.75-7.5 km/h, so somewhere between a very slow walk and a very, very slow jog.
Plus, the skateboards they are using are not going to be regular ones but purpose built and similar to downhill longboards.
You're righht on special skateboards, I have couple long distancne boards and they special brackets low to the ground with larger wheels. Makes huge difference over standard skateboards or longboards.
It's very niche market, making those boards relatively expensive https://www.gbomblongboards.com/ But for 10+ miles rides worth it.
Now I actually wonder what is the efficiency for skateboard.