As a security researcher professional, this is entirely inappropriate. He should have contacted Apple during the beta release cycle and gotten it fixed. If Apple needs more time to fix it, and is aware of the issue, then you keep the vulnerability under wraps so that other hackers do not exploit your vulnerability while it has no fix.
The only reason to publish a vulnerability with no fix is if the vendor WILL NOT FIX the vulnerability. I doubt that is the case here. This Wardle is seeking attention, and should be looked down upon.
See the guys listed here? These are the true professionals, they did it right.
https://support.apple.com/en-us/HT209139