There's a lot of factors that could play into this. First of all, anticipation itself is still being called into question. Most of the diseases we say experience anticipation are due to epigenetic factors or trinucleotide repeats. It seems likely that epigenetic-related diseases like cancer experience anticipation, but there's shaky evidence at best that trinucleotide repeat expansion diseases truly experience anticipation. If that's the case, Huntington's may very well still be with us far into the future.
Assuming anticipation is real, however, things would still take time. Who knows how long it would take to completely eradicate a disease because of earlier symptoms. With genetic diversity, people can live longer with these diseases than expected, with varying degrees of severity. It's not very likely that every generation will consistently die one year earlier than the last with slightly more severe symptoms.
