I suspect we won't see many actual new Corps. We may see some "corporate reshuffles" where the same Corp gets a different ID card, or even splinter factions within a Corporation that have potential design space while still drawing upon the existing factions. You mentioned subsidiaries, and that's a great idea. To do anything else could screw up the future distribution.
I see them releasing potentially one more Corp down the line (CyberSolutions, Inc.?) like Call of Cthulhu did with the Silver Twilight Lodge, or maybe two if they're feeling frisky, but I believe we'll just see new ID cards for the same Corps in the same way the Runners will simply have different individuals at the helm.
I hope the cards reach you soon!
Oh I don't see it as new corps, but something like:
Type: Identity: Head of PR
Faction: Corp NBN
Pay 1 click, 1 credit to remove 1 Bad Publicity
Minimum Deck Size/Influence Limit: 50/10
So it would still be an NBN identity, use all of NBN cards, but change the deck creation whilst giving a new ability.