If Reibold was working for the Nazis then why would his family have been killed in the death camps? If anything his family should have been protected. Unless they are essentially rehashing his character from Rogue One and he's being forced to work for them against his will. I also find it interesting too that like Crystal Skull Indy is aiding the enemy in some way- remember Indy not exactly fighting back when they are captured in the Jungle by Cate Blanchet. That never felt right to me. The fact that Mutt tried to get them out of that mess felt weird. Anyway, while I can understand the U.S. wanting to get their hands on the device before the Russians, it seems unlikely that Indy would become close friends with a Nazi scientist, unless Riebold intended to defect from the German side. Idk. It does seem like a plausible plot outline, and I'm not entirely hating it, nor am I really loving it either.
The other thing that feels off about it is that there is no link to ancient artifacts other than a vague reference to Atlantis. Which also brings up other questions. Time travel feels more sci-fi than serialized action adventure like Indiana Jones. I think tonally it could end up feeling not quite right for Indy. There does seem to be some religious element in the McGuffin that has personal significance to the people who made/ discovered it, and Indy has no reverence for the item in question. He might respect it's historical significance and he might be awed by its power, but ultimately he's not attached to it emotionally.
I think it's clear that if there is any credence to this leak, and the spy pictures are clear that there will be at least some CGI de-aging, which I'm thinking runs the risk for some really uncanny valley going on. Plus if any time travel element is involved it would certainly line up with the idea of rebooting the franchise with another actor so that they can tell other adventure stories within different times rather than having to adjust the story to account for Harrison's age. In essence if this pans out then they have the chance to do a soft reboot of the Indiana Jones movies, which I'm not cool with. I'm also keeping in mind that this is all rumor at this point so this is me just theorizing.