Considered doing the migration via Liquibase? I dont know that it supports parallelism in the migration process but you could do most of the rest in it (pre/post migration scripts, rollbacks, test cases (within precondition changesets), etc... Not a real programming language though; its xml config files or annotated SQL scripts...
I found that liquibase doesn't really support rollbacks, particularly with mysql as you can't do transactions for schema updates, if the migration fails in the middle of an update it just gets left in a half-updated state.
Liquibase does support rollback DDL with MySQL; I used it.
I put each DDL in a Liquibase changeset with a corresponding rollback DDL I constructed by hand. If the Liquibase changeset failed, I could run the rollback for all the steps after the "top" of my wish-I-could-put-them-in-a-MySQL-transaction operations.
But you are right MySQL itself doesn't support transactions for DDL and that is true whatever tool you use.
It is true that if you put multiple SQL operations in a single Liquibase changeset that are not transactional you can't reliably do rollbacks like the above.
It is also true that constructing an inverse rollback SQL for each changeset SQL by hand takes time and effort particularly to ensure sufficient testing, and the business/technical value of actually doing that coding+testing may or may not be worth it depending on your situation/use-case.
I hadn't heard of Liquibase until now. Taking a brief look, it doesn't seem like it would be suitable though. For large scale migrations you really need to be able to express arbitrary logic ("migrate A to B but only if file X on the file system contains Y"), which you can't do with something like SQL or XML.
