VTI won’t really be affected by this.

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.

NVDA is like 8% of SPY and 6.7% of VTI. So these mega tech stocks are less dominant in VTI, but it's not a night and day "won't really be affected" kind of difference.

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.

The index they use is altering the rules. I complained to my account rep, he agreed it was not great and is asking the fund mgmt what the plan is. I doubt there is a lot they can do.