A capsule is irrelevant. To get to 750mph they actually have to get a track that can mitigate all known and unknown physical problems that stop trains nowadays from even going over 350km/h during operation. Showing a mockup does nothing to address hyperloop's baseless promises and simpsons monorail reenactment. To put it in perspective, its as if they showed a supersonic jet when they didn't even recognized the existence of sonic booms.