I am not sure if Commander Rex could live much longer. The clones had genes that allowed them to grow at an accelerated rate, so five years after Endor (which Star Wars said Rex as on the forest floor) would probably make him cane walking old.Fridays episode (Chapter 13) is written and directed by Dave Filoni, so I have to think this would be Ahsoka’s live-action debut. The last episode Filoni both wrote & directed was Chapter 5: The Gunslinger, where we got a glimpse of a mysterious figure in the Tatooine desert standing over the body of the mercenary played by Ming-Na Wen. It was assumed that this was Boba Fett, but I personally like the idea of this being Commander Rex. That would allow Finoli to continue the story of Ahsoka-Rex and it also gives a reason to go back to Tatooine in later episodes or spin-off series. There’s not really a reason for Djin to go back to Tatooine if this isn’t the case.
As for these figures that we have seen on Tatooine in Season 1 and Season 2, I have no idea who they could be. I presume they are just more bounty hunters working for the Empire being a step behind Mando.