Apple has made it abundantly clear to the world on the page you linked and WWDC and press releases and on-the-record interviews with the media that the iPhone 15 Pro Max A17 Pro is compatible with the fall arrival of some manner of a beta implementation of Apple Intelligence.
- Apple Intelligence will be available in beta on iPhone 15 Pro, iPhone 15 Pro Max, and iPad and Mac with M1 and later, with Siri and device language set to U.S. English, as part of iOS 18, iPadOS 18, and macOS Sequoia this fall.
Some features, additional languages, and platforms will be coming over the course of the next year.
I would plan on Fall last week in December or maybe a month earlier but not on iOS 18.0 but you never know what Apple will decide. If fully released means the last iOS 18.x in May of 2025 you probably will have most of what was previewed and possibly some unannounced surprises on your phone.
I hesitate to offer any other opinion on what some features come later, what some platforms come later in 2025. I would emplasize that Apple has left a lot of wiggle room in their plans to declare what it was they promised, so I look forward to seeing what happens in the next 4 to 5 months.
So no, you should not expect everything previewed if your definition of fully released is the initial fall release of iOS 18.0.