From IRC:

[...] currently it looks like this:

• Blueprint calls SchematicFactory -> SchematicFactory checks factoryID -> calls SchematicFactory of type factoryID -> SchematicFactory gets the correct Schematic class instantiated -> sets the block ID and meta inside it -> returns the Schematic

the new system would be:

• Blueprint gets Schematic ID string -> SchematicRegistry gets the Schematic instance -> the Schematic instance initializes the block ID and meta via readSchematicFromNBT as it should be