Personally I’m hoping for an iMac 6K which would be a ~24 megapixel display device. Of course an iMac 8K would be jaw dropping, and able to display almost in their entirety images from the vast majority of cameras on the market. But 8K is not likely, nor is 6K—yet.
And then there is the sad old 2013 Mac Pro. Mine is still going strong. But maybe Apple will just cancel it instead of releasing a new Mac Pro?