1. Can't they already do this (ie. favoring sites that have google issued certificates, or are hosted by google CDN) today? What does supporting multi-certificates have anything to do with it?
2. Google isn't a transit provider. Therefore they aren't really in a position to abuse their position to MITM traffic.
3. Google already controls the chrome browser itself. If they want your data they don't have to MITM you, they can just upload it after it's been decrypted by TLS
1 they do. and get backlash when they do it more openly, e.g. amp
2 they already do things like hitting THEIR dns servers for all links on a page you're reading "for performance". you have no idea what is in play here if you think "omg google is going to phish me my bank password with a fake login page". you're way out of your water here.
3 they can't because of backlash and that would move people to other browsers. they have to slow boil you. see point 1
2. Google isn't a transit provider. Therefore they aren't really in a position to abuse their position to MITM traffic.
3. Google already controls the chrome browser itself. If they want your data they don't have to MITM you, they can just upload it after it's been decrypted by TLS