There’s been rumors of Apple working on M-chips that have the GPU and CPU as discrete chiplets. The original rumor said this would happen with the M5 Pro, so it’s potentially on the roadmap.
Theoretically they could farm out the GPU to another company but it seems like they’re set on owning all of the hardware designs.
TSMC has a new tech that allows seamless integration of mini chiplets, i.e. you can add as many CPU/GPU cores in mini chiplets as you wish and glue them seamlessly together, at least in theory. The rumor is that TSMC had some issues with it which is why M5P and M5M are delayed.
Theoretically they could farm out the GPU to another company but it seems like they’re set on owning all of the hardware designs.