1) Short selling more stocks than actually exist is (iirc) against the rules in most countries so there's that.
2) Treating retail traders and hedge funds differently in their access to the market is another area.
3) Margin requirement changes. Margins get bigger and bigger, until a disaster happens, then they get smaller, then they creep up again. It is a never-ending yoyo. I personally would rather see a tax law change that makes margin trading less attractive rather than put stricter limits on margins, but that is just a pipe dream.
4) A corollary to #3: making sure brokers have more cash on hand or at least more credit available so that they don't have to stop retail customers from buying. See Robinhood not having the money to let customers buy GME yesterday.
5) Enforce the laws on hand about publicly pumping and/or trashing stocks. Stricter crackdown on the illegal handshake agreements to manipulate markets. There has been almost zero criminal punishment for the whole 2008 crash--it is time to actually take a stand for what is right. If corporations, like banks, are people then arrest the leaders that break the laws like other people that break laws.
6) Capital gains tax changes. This is another pipe dream. But, I don't see why short sellers, hedge funds, etc. should pay low (0%, 15%, or 20%) capital gains tax. Their role in the economy isn't worth the tax break we give them. Instead, limit capital gain tax breaks to those who invest in startup and growing companies--you know, those who are actually making the economy better.
7) Reduce the perverse incentives to give retail customers a bad deal (payment for order flow, high speed trading, massive fees, lack of fiduciary requirements, etc).
