I think this issue still actual in 2020. The problem that new games nowadays utilizing more actively shader cache and default 128 MB value appear to have been an inadmissible. For example Borderlands 3 game can easily utilize 500 MB of shader cache and game have horrible experience because of stutters even on decent hardware. But with with __GL_SHADER_DISK_CACHE_SKIP_CLEANUP=1 tweak it runs absolutely fine.
I understand that there could some reason to stick with default shader size values but from my perceptive this looks like nothing could be worse if we stick with 128 MB cache size. Unlimited cache probably not the best solution either. So why not change it to 512 MB or even 2 GB by default?