What would be the implications of ETH becoming a security?

I just saw this post about VanEck and ProShares dropping their ETF applications and now there's speculation that it may be because they suspect ETH will be deemed a security. If ETH is deemed a security what are the implications of that? Does anything actually change?

• Can't an ETF be made even if it's a security? If yes, why would they pull their application? If not, any other idea on why they'd pull the application?
• How would ETH being a security affect users? Developers? Investors?
• Any changes to tax requirements?
• What does this mean for projects (in the US)? Would they legally be allowed to publish contracts (like Uniswap v2) that don't have a whitelist/blacklist?
• What does this mean for ecommerce businesses that accept ETH or companies like BitPay?

Feel free to mention any other ways things would change.