It remains to be seen whether they will actually hold the private key for that intermediate certificate and issue end-entity certificates from it, or if this is

It remains to be seen whether they will actually hold the private key for that intermediate certificate and issue end-entity certificates from it, or if this is just some sort of reselling deal where a different, trusted CA holds the key, performs domain validation, etc (which is a fairly common practice). I have my doubts about whether Mozilla will accept them continuing to operate an actual CA with a new cross-signed certificate prior to them completing the inclusion process. CAs need to disclose these intermediate certificates, and I expect it would end up being revoked, with possible sanctions for whoever cross-signs them.