According to The Verge, Harrison only spoke briefly about the publisher-specific offerings, so we don't have many details. He did say they'll likely live on top of the Stadia Pro subscription, as a kind of premium add-on. Rock Paper Shotgun likens it to buying HBO on top of an existing cable package. Harrison also suggested that this model will work best for publishers with larger catalogues. So far, Ubisoft, Bethesda and Square Enix have the most Stadia titles lined up. Theoretically, we could see subscriptions from those publishers first.
The $9.99-per-month Stadia Pro subscription doesn't allow you access to all Stadia Games, so a publisher-specific subscription could be a good way to play a variety of your favorite games without purchasing them individually. But it could also make Stadia's subscription plans overly complicated, and it adds yet another monthly subscription for gamers to consider. It's unclear when Stadia might launch the publisher-specific plans, but Harrison said publishers may start thinking about them "in relatively short order," we assume that means sometime between now and November.