The question is how far he can get without Apple's documentation. On the CPU side, probably pretty far as they use the standard ARM ABI. On the GPU side? This is where things will get really hairy. Same with the machine learning cores.
I'm not planning to get a macbook. My main contender would be an XPS with a new ryzen cpu on 5nm, if they'll have one next year, or a thinkpad again with Ryzen 5nm. I would not accept anything less.
But thinking about it, it might be that the mobile AMD CPUs are a year behind the desktop ones. So next year the best ryzen could still be at 7nm Zen3. In that case apple will have a 2 year transistor lead. But, will see.
Only wishful thinking from my side. As mentioned in the post, I hope that the M1 performance and aggressive apple marketing will push premium pc laptop manufactures in adopting the best performance x86 CPUs. And I also hope that AMD will seize the opportunity to get a good chunk of mobile market.
Of course, next year laptop models are probably being finished right now, and it could be that intel still found a way to bribe premium manufactures from including AMD in their premium models.
In my opinion they'll lose marketshare if that happens. But, there are most likely smart people with a lot of more information than me making these decisions.