place limits on how many properties they can own as well, plus also close loopholes like using LLC / some kind of other shady company to buy more houses.

This is a cat and mouse game that the law, glacially paced as it is, can never win. The tax strategy suggested would be much more effective.

That's closer to trying to ban speculative investment. I guess my opinion on this is just that this type of approach won't work as well, because keeping people from participating in the market isn't a direct way to move the market. And what needs to happen is, lower housing prices and regular people having greater proportional purchasing power, so the best focus would be to give investors strong incentives to sell, increase supply, and redistribute wealth, in a way that's easy to enforce.