It’s based on the total market and not artificially limited to a small number of large companies. Plus it’s free-float adjusted so only the publicly-tradable portion of SpaceX is considered when weighting its inclusion so it will constitute only a small portion of the fund. There is also a (small) mandatory delay period which I don’t recall between it going public and it becoming included in the index which should give time for the SpaceX valuation to stabilize on something notionally realistic.
Thankfully, Vanguard and its member funds are investor-owned so are likely more resilient against someone like Elon trying to change the rules.
> Seeks to track the performance of the CRSP US Total Market Index.
The index that is changing its rules is the NASDAQ100, commonly referred to as the NASDAQ, although NASDAQ is also the name of the exchange.
Morningstar said its CRSP Market Indexes will "undergo enhancements to introduce an alternative liquidity screen", making it possible to add SpaceX and other giant IPOs to these benchmarks more rapidly. The funds that use the CRSP indexes as a portfolio benchmark include Vanguard's $607 billion Total Stock Market ETF.
And most index funds including Vanguard track an external index. So when the index changes the rules, Vanguard changes what it buys. Vanguard is also famous for always siding with the management, they take the activist side of any debate approximately 0% of the time, so don't expect them to be fighting this for you.