Summary: 25mm internal width hookless is no longer allowed to run 28mm tires, in accordance with existing ISO standards which Zipp had previously ignored.
Zipp has three tiers of wheels and only the budget tier is not 25mm internal width. Expect Zipp and other brands to redesign with narrower rims for the next model year.
Zipp is in a terrible situation. They're going to have to update their consumer tire width recommendation to align with the UCI ruling. If they do not, they're going to be sued by every person who crashes starting from today, accusing Zipp of knowingly ignoring ISO safety standards. Expect a class action lawsuit incoming from current wheel owners demanding free new wheels, accusing Zipp of selling them a product that knowingly ignored ISO safety standards.
I had a quick look on the Zipp website and they are still showing all major brand 28 mm tyres are compatible with their 25 mm hookless rims. I expect they will be forced to revise this compatibility chart to avoid future legal issues.
Also agree this probably spells the end for 25mm hookless road rims. At least while 28 mm race tyre width is still considered the optimum.