That's so cool if it isn't weird to ask are there any current early stage companies you think have the potential to become like Tesla? Asking for a friend :)
If you're asking very broadly "where would you invest early stage today to realize explosive investment growth due to the size or value of the total addressable market," I don't have a specific company or domain answer to that. Speculative investments have a domain expertise component (know what you're investing in), a timing component (being early or late is the same as being wrong, see Webvan circa 1996-2001 vs Amazon), and a luck component (you can do everything right and the trade moves against you through no fault of your own). Charlie Munger once said:
“You’re looking for a mispriced gamble. That’s what investing is. And you have to know enough to know whether the gamble is mispriced. That’s value investing.” ... “You should remember that good ideas are rare — when the odds are greatly in your favor, bet heavily.”
So, to maximize success, know how to spot opportunity when it crosses your path, maximize those opportunities, and maximize exposure at the opportunity. Being lucky doesn't hurt. Good luck.
(not investing advice, i am just an internet rando)