If they have legitimate promise, there should be private investors looking closer and stepping forward. If they deliver on half of their boasting, they will be rich. I don't like the idea of government subsidies for flashy salesmanship and emotional attachment.
I was a skeptic, but I'm coming around. Not about Tesla, exactly, but the electric, self driven trucks. When/if the self driven gets resolved, the rest will follow. I say this from looking at electric bikes. The battery tech is already good enough, and the motor is already developed. The rest is standard engineering. But I wouldn't put any money in Tesla.
Their business model is all about hype, and while that is great for luxury goods and attracting investors and subsidies, the real applications for this are just boring. So I don't have much in terms of long term hopes for Tesla. I think Cummins or Case will make better use of the tech.
There are lots of shorter range delivery truck jobs that will benefit far more than typical long haul trucks. For that matter, the rail system could use this tech better. Why use trucks to cross the plains when rail could do it so much cheaper and more efficiently? When this is fully developed, I expect slow, solar powered rail to become the backbone of a star configured distribution system. Currently labor, habit, speed and logistics are the reasons for our system. When slower means much cheaper, and labor can be removed, habits and logistics will correct for these.