I think you can lump in Merchants and Citizens into one book, same as Drifters and Rogues - whereas Merchants make their trade by buying and selling goods, Citizens make their living by hawking their own trade skills (so, for instance, a Citizen with a free trader could set up his ship as a mobile tailor's studio and convert part of the cargo bay into his workshop).
Likewise, you could, in principle, llump together Entertainers and Nobles - both are larger-than-life personalities with vast egos that can only be assuaged by the adulation of millions of Little People. Only one difference: Entertainers work hard at entertaining the people, and Nobles only work hard at irritating them.
I forgot Scholars. They would seem to warrant a supplement all of their own - including a section on Research in Traveller, bringing the old rules up to date by incorporating rules on the online research process.
H'mm. Since journalism is considered an Entertainment sub career path, you might need to include a bit on investigative journalism in the Entertainers book too - and if so, because they're essentially both research and investigation tasks, and since journalists and scholars both rely upon their notes getting published, maybe then you could throw in Scholars with the Entertainers and Nobles, too.
You've done Psions, of course, and the military and quasi military careers of Army, Navy, Scouts and Agents. So really, the above pairings are the most logical ones available for the next careers books, IMO.