There isn't really a reason to expect a significant effect, in practice, Tesla COGS/unit plateaued a few 100K ago. It's a bit too abstract and high-level.

Batteries specifically does make sense, ex. Model X has 100 kWh battery. if I price out 100 kWh at $200 right now (high) and its $100 a decade from now, about $20K.

"Software" is hand-waving.

Electric motors being easier does make sense.

You can say the same thing about any product mass produced.

Not everything has the same unit economics. The self-driving software is one part of the costs that is heavy on the fixed costs side and will therefore scale better than other costs. If you produce a million cars vs one car, the cost to make that software isn't a million times more expensive.