I'm not even sure if the performance race is going to endure - Sony continues to hold the home console crown, Nintendo prints money with their hugely outdated Switch, and Microsoft appear to be pivoting to publishing more than a console exclusivity race they will probably never win ("going Sega")
As you said, the future of x86 isn't guaranteed, but if I were calling shots I'd look at Arm designs with embedded graphics like Exynos and Snapdragon before trying to build a fully custom design based on POWER and graphics from elsewhere (probably still AMD, and that single-source has been compelling enough to adopt even while the CPU performance was lackluster)