alt Hacker NewsFor anything major you're right, you'd expect them to be on the HSTS preload list in people's browsers which forces all requests over SSL which would then pick up an invalid certificate. That doesn't make this harmless though, just being able to blackhole traffic for something is a pretty significant attack - Pakistan a few years back accidentally caused YouTube to be unavailable ~worldwide when they only intended to make it unavailable within the country. There's also a lot of sites not on the preload list, and those you could fairly easily MITM, especially if you've also got access to a tame certificate issuer and I don't doubt that a nation state could persuade someone to issue them some certificates given the proper levers.
Only as long as all certificate authorities ensure that all networks they host servers on secure. If you can BGP spoof a domain-validating CA, you can get a valid certificate for any domain of your choice (unless maybe if that domain is DNSSEC-enabled, the CA does strict validation, and the domain has a CAA record for another CA that is not BGP-spoofable).
Major news outlets, government websites from various countries, the American army, and many more all lack CAA records, for instance. Any CA can generate a valid certificate for those domains and it's up to the people watching the public certificate transparency logs to catch any malicious certificates.