John Watts, I hope Mongoose does that also. I know you've been in communication with them, but you can't say much about it. Best of luck! I don't want anything to happen to Cepheus.
This is all purely conjecture on my part:
Matt, and Hunter before him, could not have released any text thru the OGL without Marc's permission. Therefore, Marc approved of that. Open Source and the OGL was the big thing at the time. Clement Sector, Outer Veil, and many other settings and expansions were made using Mgt1e and the OGL. While those did not put any money into Mongoose, it's hard to see how they kept Mongoose from making money, as Mongoose put out a lot of products during MgT1e.
When Matt made MgT2e and changed the license, Marc would have had to approve that as well. (Maybe they didn't think something like Cepheus would be created, but anyone following the OSR movement should have known it was possible.)
If Mongoose only allows MgT2e to be used under a new license, and de-authorizes the earlier SRD (and thus Cepheus), Marc would presumably have to approve that also. My opinion is that Marc should know that this will not be good for for the Traveller brand name. Just as WotC's name is tarnished now.