Some directories are accessed more frequently than others and I would like to keep permanently cached on the SSD. Is there a way to achieve this with Rclone.
You are right but I think that as long as there is space in cache and nothing has to be evicted then expiring cache only means that cached file will be checked against source. If nothing changed it will stay in cache. So practically frequently used items can stay in cache forever without downloading them repeatedly every time they expire.