[loeg]

It is not obvious that excluding SpaceX is (1) better for index investors or (2) what index investors/buyers want. Passive index investors buy the whole market. For better or worse, SpaceX is (will be) part of the whole market.

Most indices will be buying proportionate to float, which is probably the correct thing to do. Only the Nasdaq 100 isn't float-weighted, and there's just less money in that index than the S&P500 (even with outsized weighting, Nasdaq 100 indexers will buy about 0.5% as much SpaceX as S&P500 indexers).

[lucketone]

Eventually buying spacex is obvious and correct. Buying prematurely is questionable.

[loeg]

It is not obvious that SpaceX's price will fall (and not instead rise) between the IPO and whatever date you have in mind.