I have some really good news for Alembic users.
In the two years since we first released Alembic suite of tools, we have learnt a lot about how Alembic performs in the real world. One thing that has come up with some of our larger clients, was that the performance of Alembic leaves a bit to be desired when dealing with very deep scene hierarchies and/or thousands of scene nodes.
But a new development is coming very soon that will fix the slow initial load time of Alembic.