I just think from a marketing standpoint it doesn’t make sense to have competing TV series based on Mandalorians. Boba Fett is a fan favorite character that will never live up to fan expectations in the TV universe. I think it makes more sense, especially given the Thrawn reveal, that this clone has to be tied to the animated universe rather than Boba Fett.Rex is semi-officially in Return of the Jedi. The Mandalorian is only a few years later, so it would not be out of the question. I do agree, though, that that mostly-hidden figure was supposed to be Boba Fett.
https://www.slashfilm.com/dave-filoni-confirms-captain-rex-in-return-of-the-jedi/
Plus, Cara Dune said that she fought on Endor, so a reveal of Rex would tie Dune and Ahsoka together for a future plot line and/or spin-off series which has already been rumored to be in the works.
I suppose an outside possibility is Commander Cody. Perhaps he’s searching for Obi-Wan’s home on Tatooine either to find some clue about the whereabouts of the remaining Jedi or to make peace for Order 66.