You can do that today by configuring mapdb to write to /tmp or whatever you have mounted as tmpfs.
But this is missing the point and big picture Even if you move mapdb, any other persistence service, any of the writes to log files, any swapping will still keep hitting your disk.
SD cards are worse than SSDs but both are affected by wearout sooner or later, and counting TBW isn’t really properly accounting for the fact that it’s always the same files/sectors on disk again and again that OH is writing to.
Check out this standard post.