IMO: There's a ton of circumstantial evidence Liquid Glass was supposed to be a 2026 feature, but at some point between 2024-2025 they accelerated it for a 2025 release. Stating that it was because of the Apple Intelligence disaster of 2024 totally fits in the timeline.
1. Liquid glass went through significant changes in every developer and public beta release between June and the full release in September. Transparency, border, light scattering changes, it was very clear that they didn't even have a strong definition internally of "how liquid" and "how glass" the liquid glass should be, and were responding in real time to reddit comments complaining about it.
2. Many aspects of the design system are still buggy, today, in October. There's some evidence that accessibility features like Increase Contrast and Button Shapes are implemented entirely differently depending on your model of iPhone [1]; they certainly do not do what the label says they should do for some users, and at the very least are implemented inconsistently, or not at all, across many apps.
3. The MacOS 26.1 developer beta further implements (welcome) changes to the design system [2]. Why weren't these ready for 26.0 GA?
4. It is expected that 2026 and 2027 are going to be a massive years for new iPhones, as we're expected the iPhone Fold to drop in 2026, then in 2027 we'll see something related to the 20th anniversary of the iPhone. Comparatively speaking, 2025 saw a new midrange iPhone model, but that's it. Coinciding a large design system change with a new phone format change (foldable) is an Apple thing to do.
If you think about Apple's timeline pre-AI, all of this kind of makes sense. A bunch of Apple Intelligence features were supposed to be done by the iOS 18 cycle, then for iOS 26 they could have continued to fill in more AI features, before a massive design refresh + new phones for iOS 27 in 2026. But they got to like iOS 18.2 before they realized that they screwed up and the AI features needed a ground-up rewrite [3] and wouldn't be ready for 18.4, let alone maybe even the 26 cycle. At that point, they realized that they went from a decent 18 month roadmap for AI stuff, to 0 months; and they needed something to make 26 interesting. So, they go to design and say "i know you thought you had 12 months until the 27 cycle, but actually, you have six, we want this in 26".
[1] https://www.reddit.com/r/ios/comments/1nx4aqe/comment/nhkor2...
[2] https://www.reddit.com/r/MacOSBeta/comments/1no2uuu/macos_26...
[3] this is not supposition - if you weren't following the Apple Intelligence drama of 2024, Apple has publicly stated that their AI had an initial v1 architecture that was demoed at WWDC 2024, but by late-2024 it became clear it would have to be thrown out: https://youtu.be/wCEkK1YzqBo?t=89