The certs were intended to be used by new US and EU subsidiaries. Those were still in the process of being set up, so the certs were never used in production for customer signing.

IIRC the Comodo AAA Services root was already in the process of being retired, with its "trust bit" having been removed by Mozilla and Chrome last year. Nuking it completely should have been a no-op for end users.

The whole chaining & cross-signing song-and-dance will never go away completely. There's just no way around if if you want enrollment of a new CA to take less than a decade, or if you want CAs to be able to do any form of non-world-breaking key rotation. Intermediates signed by third-party roots are already treated with the same scrutiny as root certs, so they should have been fine...

But yes, this will undoubtedly result in even stricter verification. For example, some participants are already calling for mandating attestation that a key has been generated inside a HSM running the right config.