I guess quad core with good enough integrated graphics will be a part of Cannon Lake or Ice Lake since the less heat produced with the 10nm manufacturing process will make it reach low enough temps to fit into the thin bodies of the current lineup. Most of the Kaby Lake revisions with quad core you are seeing now being launched have included a dedicated GPU and most of the models are being released with Nvidia Geforce MX150 or likewise. Heat is still a problem in all 15" with four cores, the fans are never idle and spin continuously at 2000rpm.
If I was Apple I would wait for 10nm in order to avoid problems with heat. The increased potential shown by Intel is probably done with a dedicated cooler on a test bench, and results may vary with different setups concerning space, heat and the builds ability to lower temperatures. One thing is to have the technology, the other part is to make the performance durable and portable.
Most of the machines you will see on the market with the new Kaby Lake S quad cores may also have loud fans and most of the laptops are geared against gamers that also endure quite loud spikes in decibel on their desktops as well as their laptops. They may not be so sensitive to high pitched fan noise from hot components in stark contrast from the average Apple buyer. Mac users have a tendency to uncover all flaws with their computers from launch day one.