It seems obvious in retrospect, but the fact that SpaceX will be "valued" at $1.75 trillion after the IPO is irrelevant when only $75 billion worth of its stock will be publicly traded.

$75 billion in float-adjusted market cap puts it around 180-190th in the S&P 500. So sure, it will likely get in there eventually, but there's no rush to bend the rules to get it in right away.