I think you're mistaking the general concensus a bit. There's a fair bit out to suggest that the rotation will actually be CL-on and not BW-on. No one knows for sure but:
The 2012 Professor Cup is a CL-on format where basics are banned and stage 1s are basics, stage 2s are stage 1s. Now... granted that this isn't the same format as modified constructed, but they do acknowledge that CL is a different series from HS, and TPCi did create a format that rotated from CL.
So that would let us keep key supporters, some trainers and some babies, and special dark and metal energy. There was a lot of curiosity about why they wouldn't reprint Special Dark in Dark EXplorers, if they were planning on keeping it in the format. Well either Special Dark will be reprinted later, not at all, or it doesn't need to be because CL will provide it.
Just food for thought since this discussion is already assuming it's BW-on, and that's not necessarily the case.