Alexander Zaytsev created an issue — 6th April 2017, 14:16:19:

hbm2ddl was heavily refactored in HHH-9490/HHH-9492. We need to port these changes.

Frédéric Delaporte added a comment — 6th April 2017, 16:44:33:

HHH-9490 only looks as a "done at the same time" issue. HHH-9492 seems to be the actual issue having triggered those changes.
It is not only about changing the metadata handling, but also the whole bootstrapping process (deprecating Configuration class).