AHI is probably a subject to removal. It's clear that managing a hash table costs some performance but it's not clear where it could be beneficial.
One example of harm was found in https://jira.mariadb.org/browse/MDEV-16796 where TRUNCATE was slowed down.
Axel Schwenke please find cases where AHI improves server speed. Then we can measure whether it's needed at all or not.