But then what? Given the number of accounts Google has, odds are that nearly every alphanumeric combo less than 8 or 10 characters plus “@gmail.com” is a google account. This vulnerability gets you other domains, but still not seeing it. Massive databases of email addresses are a dime a dozen.
The only angle I can imagine is phishing for high profile creators, and at most this is a “makes it easier” and not a “creates the problem” bug.