Three problems with this:
1. Removes the pain of age verification, encouraging some people to stay in the proprietary walled garden when everyone would be better served by open platforms (and network effects).
2. Provides a pretext for more invasive age verification and identification, because "the privacy-respecting way is too easily circumvented".
3. Encourages people to run arbitrary code from a random Web site in connection with their accounts, which is bad practice, even if this one isn't malware and is fully secure.
> everyone would be better served by open platforms
Oh cool, which ones?!
…aaaand there's the problem.
Proving that something is possible doesn't mean encouraging it. This was a beautiful work of reverse engineering, that shows how hard it can be to verify personal data without invading privacy. I prefer this awareness to blind trust.
The code was released, therefore it is not arbitrary (problem #3). Should companies react with more invasive techniques (problem #2), users can always move to other platforms (problem #1).