What makes it a risky investment, in my opinion, is the fact that once the production/price/market variables become favorable for the technology, the big companies will be able to scale it at a much lower cost, as that is what they are good at.
I very much doubt that Tesla is going to outsource its manufacturing for key components. It is going to keep those in house, and it will be expensive in the near future, but they will not have worry about competitors getting cheap access to those components. Too many of the current car companies are focused upon assembling a car; they are not engineering huge advantages in technology or going in new directions.
Tesla is going to have these guys beat for no other reason than they are going to sit on their hands until it is too late. If you want a better explanation, they are going to have engineer their own product and manufacturing of specialty parts. They don't seem interesting in committing to electric cars now and when Tesla is big enough to be mainstream it will still take them 3 to 5 years to get their own product out the door.