If Nvidia gets to a point where they have to onboard their GPU to keep scaling, I don't see why they couldn't do it. They design their own SOC packages now, and have been integrating Nvidia IP into third-party chips for well over a decade. Once the need arises for "Nvidia Silicon" beyond what we see in Tegra and Grace, I wager we'll see it.
From a cynical perspective, Apple's focus on integrated graphics kinda kills any hope they had of scaling to Nvidia's datacenter market. I mean, just look at stuff like this: https://www.nvidia.com/en-us/data-center/gb200-nvl72/
GB200 NVL72 connects 36 Grace CPUs and 72 Blackwell GPUs in a rack-scale design.
Tightly integrated packages do work wonders for low-power edge solutions, but it simply doesn't enable the sort of scaling Nvidia has pulled off as fast as they've done it. CUDA is certainly one aspect to it, but Apple had the opportunity to make their own CUDA competitor with OpenCL through Khronos. The real reason Apple can't beat Nvidia is because Apple cannot write an attractive datacenter contract to save their life. Nvidia has been doing it for years, and is responding to market demand faster than Apple can realize their mistakes.