DKIM, SPF, and DMARC only reduce spam which is sent from misbehaving email servers/senders. But those standard don't stop spammers who send spam from email services like Gmail and iCloud, and from corporate email accounts whose credentials the spammers stole. All those email servers have perfect DKIM/SPF/DMARC records. And yet, I see a lot of spam coming from Gmail, iCloud, and corporate email servers.

Standards rise and fall; corporations and nation-states can't stop people from switching from one protocol to another. The reason email hasn't been replaced is because a sufficiently better replacement has not been made yet. And if that replacement was good enough, corporations and nation-states would switch too.

See my other comment for an incomplete description. In short, my idea was to make a completely different protocol to replace email.