There are a lot of postgres fans on HN, would you mind giving some more info on why you want to go from PG to MySQL?
At 80% of completion, I moved to mySql because I needed spatial index, I installed Postgis but got a lot of problems with doctrine-migration.
The transactional DDL seems to be introduced in MySQL per 8.0 though
I thought so as well from the release note wording, thanks to theptip for confirming in the docs that DDL is not transactional in 8.0, just crash-safe. see https://news.ycombinator.com/item?id=16876549.