MariaDB has offered online schema changes in InnoDB for several years now with continous improvement.

Their (currently commercial only) engine, Xpand (previously known as Clustrix), offers distributed SQL as well as online schema changes.

No need for an unncessary database migration if you are already on LAMP and the like to get these fancy features. However handling any kind of change should be handled with care, especially on such a large dataset. Test your rollback procedures!

Disclaimer, I work for MariaDB.