More over, maybe Apple us working with AMD and NVidia to ensure compatibility between their GPUs and the A series chips.
We won’t know until next year I bet.
At this point the most likely outcome is that Apple will rely on their own integrated GPUs. They certainly have attained a reasonable (decent) level for their consumer Macs already, I suspect they have the higher level iMacs and 16" MBPs covered too. The question mark is for the Mac Pro.
My personal bet is that it will have a decent integrated GPU too which will make it suitable for Audio professionals and maybe developers, the mystery is what they do for high end video, animation, CAD etc. I'd bet on more FPGA cards along the lines of the Afterburner if I was forced to bet right now.