This integration is way more limited and frictioned. Whereas with search Apple's fully outsourced and queries go straight to your 3rd-party default, Siri escalates to GPT only for certain queries and with one-off permissions. They seem to be calculating that their cross-app context, custom silicon, and privacy branding give them a still-worthwhile shot at winning the Assistant War. I think this is reasonable, especially if open source AI continues to keep pace with the frontier.
The trendline is definitely toward increasing dynamic routing, but I suspect it's more so that MoE/MoD/MoDE enable models to embed additional facts with less superposition within their weights than enable deeper reasoning. Instead I expect deeper reasoning will come through token-wise dynamism rather than layer-wise -- e.g., this recent Quiet-STaR paper in which the model outputs throwaway rationale tokens: https://arxiv.org/abs/2403.09629
For now.