Hi, dev-python/sqlalchemy-1.3.17 still has an optfeature line for dev-python/mysql-python which has been removed from the ::gentoo repository. The pure fork for it is dev-python/mysqlclient so you should test it works similarily to mysql-python, and update the optfeature line. 1.3.20 seems to have correct optfeature line updated.
Last version referencing mysql-python was removed in commit 33ff0e9b680f2744d4bd233a497d05923469e41c.