If there weren't so many rumors or reports about Apple transitioning to their own ARM based solution starting in 2020 (or 2021), I would have said it is strongly possible for Apple to use custom AMD solution for their Macbooks. When Apple switches CPU vendor, i would assume that Apple should be committed for at least 5 years when it decides to do so. I can't imagine Apple switching for AMD for short term stop gap solution before changing to one of their own A based ARM solution. If Apple indeed starts using AMD for their macbooks or their other product line, then I would assume they might have scrapped or delayed ARM transition for several years at least.
There are NO rumors about Apple shifting to ARM, but all of the rumors said that Apple will shift to their OWN, designed by them CPUs. The matter of ARM was completely made up by community built around over Apple.
Currently, in Mac OS Catalina Beta we have ALL of AMD APUs available. Including Renoir, and Semi-Custom Van Gogh, which does not appear on any AMD roadmap. And it is first time, ever, we have AMD APU kexts in any Apple OS. What this means?
Apple needs an OS that they can test stability of AMD based machines and software, while working on next gen AMD CPU based product. That is why they have put those previous generation APU kexts in the OS, in the first place.
So yes, if Apple ditches Intel, and they do, they are switching over to AMD for CPUs. If Apple will ever use ARM in their laptops, or any computer, it will be for Chromebook replacement(education) and access to their services, extremely basic tasks.
ARM is not ready and never will be ready to offload workloads from Workstation computers, and even semi-pro machines, like MacBook Pro.
In the first paragraph I said that Apple will switch to their own, designed by them APUs. Semi-Custom can also be considered this way, that Apple designed those CPUs. The wafers will be ordered by Apple from TSMC.
I will repeat one more time. Apple is not shifting away from x86 on their computers. They are just ditching Intel. In 2020 we will see first AMD CPU based Apple computer, alongside ARM Chromebook competitor from Apple.
MacBook - ARM.
MacBook Air - x86.
MacBook Pro - x86.