Is it possible to "double up" on certificates somehow so that a service can offer certificates from 2 or more Certificate Authorities simultaneously. The goal here would be to get a certificate from CA A that might be compromised by global persistent threat X, but not global persistent thread Y, and another certificate from CA B that might be comprimised by global persistant threat Y, but not global persistent threat X. e.g. using a certificate from an American CA and a Russian CA simultaneously would likely only expose you if both the Americans and Russians cooperate to eavesdrop on you.
I kinda see what you're getting at, but that wouldn't fix anything. If I interpret what you want correctly, you basically want a cert that is dual-signed by multiple CAs which would be under different political jurisdictions. It's a clever idea, but it's not really usable. Clients validate that they trust a member in the signing chain, not all members in the signing chain, so as soon as the browser encounters a signing authority that it trusts, it will trust the cert.
Furthermore, this wouldn't really stop a bad actor from getting a cert signed by a third CA which your browser trusts and MITMing it to you, unless you're cert pinning, which practically nobody is because it comes with a tremendous list of user experience issues.
