I could see Apple working around the emulation speed issue by entering an agreement with AMD where Apple designs 95% of the chip, has AMD design an instruction decoder to translate x86(-64) to native uops for the most common instructions (only falling back to emulation for uncommon instructions), and has AMD "manufacture" the chip (so it technically falls under AMD's x86 license).

This would allow Apple to avoid much of the overhead of software emulation and I'm sure AMD would be happy to play along since it gets them a (thin) slice of Apple's margins which they would otherwise not have. After a few generations when x86+ARM fat binaries are the norm in the MacOS ecosystem they could drop the x86 decoder (falling back to software emulation only) and presto.