As for how they’ll get the chips into existing Teslas, Elon says: “We made it easy to switch out the computer, and that’s all that needs to be done. You take out one computer, and plug in the next. All the connectors are compatible.”
I'll believe it when they successfully install it to the previous gen car. More often than not it turns out that some other hardware is incompatible with software improvements or has bugs and full system is not functional anyway without full upgrade.