I understand that one major relevant issue that's been discussed is the impact of very large IPOs coupled with passive index funds and some changes to how indexing works.
A lot of people have money in index funds
these are funds that track a given index.
Traditionally, indexes tend to exclude very newly-listed companies, even if they are large, from being included in indexes. This gives the market time to place a value on the company.
Companies also not-infrequently drop in market capitalization from their IPO.
Recently, the NASDAQ-100 changed its rules so that companies are included much more quickly in the index, and are given a substantial amount of weight even if only a small portion of the shares are actually available for trading.
What this means is that SpaceX will IPO. SpaceX has a very large valuation. This will cause it to be included in the NASDAQ-100 index after 15 days, unlike the way that things had worked in the past. At that point, index funds that track the NASDAQ-100 index (e.g. QQQ or QQQM) will sell shares in companies like Apple and buy shares in companies like SpaceX. If its value drops after that, as is likely, then index fund investors will eat that loss. A lot of shares that are locked up and held by insiders will then unlock (I understand that 90 days and 180 days are significant), and so if those people then want to sell their shares, that will be likely to drive SpaceX shares down. Holders of index funds will lose some money, and pre-IPO holders of SpaceX equity will have made money.
https://www.fool.com/investing/2026/04/01/how-the-spacex-could-affect-these-popular-nasdaq/
The S&P 500 (SPY and VOO are major index funds that track the S&P 500 index) and Russell 1000/2000 index inclusion rules also changed, though I understand that the impact on index funds that track these indices is not as substantial as for the NASDAQ-100 index.
https://spotgamma.com/spacex-ipo-index-changes-spotgamma/
One concern I've seen is that if sufficient companies can be blown up to very large valuations and then IPO, operating under more-permissive index inclusion rules may degrade the returns on of index funds, since those index funds will keep buying into large IPOs and likely losing money on doing so. If this sort of thing becomes a major thing over time, it might cause investors to shift out of index funds and into active funds that merely use similar strategies (but avoid buying into IPOs).
SpaceX isn't the only company that this would affect; some large AI companies like Anthropic and OpenAI, with very large valuations, will likely similarly be affected.
Some folks on Reddit were referencing a video Ben Felix did talking about the phenomenon:
https://www.youtube.com/watch?v=iOyFja87uyw
EDIT: The basic misincentive here would be that NASDAQ controls the NASDAQ-100 index, but their interest is in getting more companies to list on the NASDAQ; they aren't interested in trying to maximize returns for index fund investors. Random company who might list on NASDAQ would actively like index fund investors to buy their IPO at a high price, since that transfers wealth from holders of index funds to pre-IPO equity holders. Operators of passive index funds (for QQQ/QQQM, Invesco) would like their passive fund to make solid returns, but they don't get to set the rules for index inclusion; NASDAQ does.
