Your math is a bit off, confusing threads & cores. 128 threads is only 4x of what AMD's top desktop CPU offers, and is what current AMD server CPUs offer in a single socket system. And over the past 20 years consumer CPUs have 32x'd their thread count. A 4x increase over the next 10+ years really doesn't seem all that far-fetched.

Also, the scaling problems show up far before 128 threads are used. The scaling issues start showing up at just 4-8 threads, depending on the error rate.

Also also, C++ is used in a hell of a lot more places than just consumer desktops. So the current limitations of consumer desktops is fully irrelevant anyway.