Migration of Classic gl to NEW GL

Hola Gurus !!!

Iu2019 m involved in an R3 upgrade project, 46c to ECC6.0. During this migration, our client will migrate from Classic GL to New GL.

After that, they will implement Bi with SEM BCS for consolidation purpose. Here is the question, they are asking us if is recommended perform the consolidation implementation after new gl come in production or if we can implement SEM BCS with classic gl and after 6 months perform a migration to new gl in ecc and then works at the sem bcs side in order to adapt the ERP changes into consolidation module.

I would like to know if you have some documentation or some guide regarding sem bcs side.

Any help will be appreciated.