I doubt we'll see more characters cross faction outside of the droids, unless the new ones come with all the command cards that the old one had. So for an Old Ben Kenobi, unless he is named that and not Obi-Wan Kenobi with "Old Ben" as the title, then the Clone Wars Command Cards would still be usable on him, just like we have with OP and CMD Vader and Luke. None of his command cards require you to have clones so they would work just as well in other armies, even if they aren't exactly designed for them, you'd certainly want the more Obi-Wan focused ones.
This then creates an issue with Clone players buying a Rebel Expansion just to get their hands on the new Obi-Wan Command Cards. The same holds true for Rex, and (although she isn't in the game yet) Ahsoka. With all the options for Rebel Heroes, with the rest of Phoenix Squad to go with Sabine, and the rest of Rogue One to go with Cassian, Jyn and K2, why would they repeat the clone wars characters, when they'll soon run out of viable alternatives for the Empire, due to that faction being less hero/villain focused in the lore.