Nvidia's AI $trillions may influence this arrangement in the near future. In the recent past Nvidia has bid Samsung against TSMC in attempts to save costs, but Apple's strategy works well for as long as one foundry has a process advantage.
Even if Nvidia also wants TSMC's latest process, that could work to Apple's advantage. Right now it's looking like Apple might end up with TSMC's 3nm process for 18 months. If Apple and Nvidia split the initial 2nm capacity, it could be 3+ years before AMD and Qualcomm can get to 2nm.
If Nvidia launches the RTX 50 series in late 2024 or early 2025 on TSMC's 3nm (which seems to be the rumor), what does that do for availability for AMD and Qualcomm? Maybe what we'll see going forward is Apple taking the capacity for the first year and Nvidia taking the capacity for the second year leaving AMD and Qualcomm waiting longer.
That would certainly benefit Apple. Apple isn't competing against Nvidia. If Nvidia uses up TSMC capacity leaving Apple's actual competitors at a bigger disadvantage, that's pretty great for Apple.