By the time solid state battery are thing, Tesla will be much bigger (and moving faster) in the EV space, so it's highly probable that the industry (including cell manufacturers) will line up to support Tesla rather than Toyota. Also, Tesla's margins are improving to a point where they'll soon be more profitable than Toyota and be able to pay a better price for any cell production capacity available (solid state or not). It's getting really late for the Japanese giant and they're still in denial (a good friend of mine is responsible for the deployment of Mirai in Europe and he's well aware that).