I have a feeling that the wide spectrum of different ways to mitigate CPU bugs will slow down the demand for a new "slow and steady" CPU architecture. Linux already comes with a feature to wipe the L1 cache on every context switch -- simply enabling this option will compete with brand new architectures for a while.

A major advantage of not adopting new CPU designs for a while is that you get to keep insecure-but-fast and secure-but-slow behavior in the same CPU by simply tweaking mitigations.