Hyperloop: See all of the problems here: https://www.youtube.com/watch?v=RNFesa01llk
Boring company: summary of issues here: https://www.youtube.com/watch?v=HBtL3qDvdZc
SpaceX: How will we fund the amount of rocket fuel required to get the stuff to Mars that can produce an atmosphere? If producing an atmosphere isn't required, then how will indoor atmosphere be maintained sustainably (financially)? Matt Damon's math didn't seem to work out in that movie...
Tesla: So far so good, but what about battery recycling? “We are at the very beginning in energy storage in general,” says Phil Hermann, chief energy engineer at Panasonic Eco Solutions. “Most of the projects currently going on are either demo projects or learning experiences for the utilities. There is very little direct commercial stuff going on. “Elon Musk is out there saying you can do things now that the rest of us are hearing and going, ‘really?’ We wish we could but it’s not really possible yet.” https://www.theguardian.com/vital-signs/2015/jun/10/tesla-ba...
SolarCity: Just look at the customer reviews so far: https://news.energysage.com/solarcity-complaints-what-homeow...
I would urge Mr Musk to focus on Batteries & long-term Tesla ownership. It would be a shame for that not to work out!
I hope this comment lasts for 5 years :)