According to the latest rumor, which definitely should be taken with a grain of salt, AMD is currently building a semi-custom SoC for Apple's next-generation iMac that would combine an x86 CPU and a powerful GPU on the one die.
The CPU component of this SoC would be based on AMD's upcoming Zen architecture, which is expected to be a massive overhaul of their processor technology that brings better performance and superior energy efficiency than their current designs. Zen chips will be manufactured using a 16nm process, so this semi-custom SoC would likely also be a 16nm part.
It's not completely clear what sort of GPU this semi-custom chip would include, but it looks like it will be similar to what the PlayStation 4 and Xbox One game consoles include: a GPU more powerful than a typical integrated graphics core, though less powerful than a mid-to-high end discrete graphics card.
Apple currently uses AMD discrete graphics cores exclusively in their iMacs and high-end MacBooks, so the two companies already have a good working relationship. AMD building a custom x86 SoC for Apple would make sense considering the path they've taken with mobile ARM-based SoCs; it has allowed Apple to have full design control over their chips and hardware.
The semi-custom SoC for Apple wouldn't be ready until 2017 or 2018, according to the report, but it would be a big change from the Intel CPUs the company has been using for years.