The Germans don’t have speed limits. As long as we have speed limits and congested urban highways, this “slowpoke” law will have marginal effect.
I don’t see the difficulty of the law making it illegal to block traffic in the fast lane, there are laws like reckless driving, obstructing traffic, weaving, driving a speed appropriate to conditions (not signs) and other laws that don’t have to be measured by a number.
I don’t think driving those nuts out of the fast lane is beyond the capabilities of modern man.