> As a novice Linux (Ubuntu) user, I am curious as to how these new changes for rand will speed up a Linux distro overall

Totally negligible. It speeds up benchmarks of getrandom() and /dev/urandom, which is a good thing, but if you were spending any significant CPU there, it was due to an architectural problem that this doesn't solve.

> It seems that, in addition to an overdue replacement SHA-1, the new code is a significant increase in performance.

No, the big improvement is removing RDRAND (arch_get_random_long) from the hot path, which only existed on relatively fast x86 hardware. (The only other arch with a non-empty arch_get_random_long implementation was s390, a mainframe.) SHA1 to Blake is only used periodically (~0.003 Hz) and probably not noticeable.