Earlier quoted context omitted.
Should one sell their 401ks ahead of the forced buying
Definitely not. What Spacex/Elon are doing is sketchy as hell. But the numbers involved here are not terribly meaningful for your portfolio. At IPO, $75B of Spacex shares will be bought/sold. The S&P 500 uses float-adjusted weightings, and the current float-adjusted total is $54T. If you are 100% invested in SPY, then about 0.14% of your holdings will be spacex on IPO day (75B/54T~=0.14%). Obviously Musk and friends…
IF SpaceX is actually worth 400-500bn and it's a few hundred billion dollars of fleece, sure, that's a "small" amount (still.. lord almighty it is never enough for these people). But the hazard is that it is a fleece. That would shake confidence in the system, the bear case is basically unlimited at that point.