you will use mongodb (like a federate engine), or you will port the tokudb to mariadb (like a innodb engine)?
i think the tokudb is being implemented today there's a MDEV in jira, for it at least (
https://mariadb.atlassian.net/browse/MDEV-4507)
i don't know about tokumx it's a engine to mongodb, or a query language (like a full text index)?
about others doubts i don't know, must check with others users or run a test database