What's your discount rate for Tesla? Now, taking that into account (profits past a certain time period are essentially discounted to 0), over what period of time should they realistically collect that money for the valuation to make sense?

It is not specific to Tesla.

https://en.wikipedia.org/wiki/Present_value

If we assume a 3% inflation rate, 2030s earnings need to be discounted by 34%. 2040s earnings by 56%. And 2040s earnings by 71%.

As you can see, even 2040 earnings still have a substantial impact on today's value.

Erm, I know what present value is. The discount rate for Tesla is not 3%, unless you think it's a risk-free asset (it's not).

   unless you think it's a risk-free asset

And unless your risk aversion is zero. Which more or less holds true for me. (Aka, playing a game of coin tossing where head wins a dollar and tail loses a dollar does not make me uncomfortable).

Otherwise it depends on:

1) Your risk aversion

2) The percentage of your portfolio you intend to invest into Tesla

3) How correlated your portfolio is to Tesla

If you only invest a sufficiently small amount (compared to your overall portfolio) into something, then the overall risk of your portfolio will go down. No matter how volatile that something is. So in that case, there also is no need to discount future earnings except for expected inflation.

That’s true, but the amount of discounting goes up with the years, in the limit to 100%.

If I borrow $100B and promise to return it in 50 years time, you likely would want $200B back, even if you were 100% sure I would pay it back.

Not necessarily! German government debts, even the long 10 year ones, have ventured into negative interest area.