One pretty reliable source says that the mazda I6 engines are destined for longitudinal mounted Lexus cars. First to show up in the 2024 4th gen IS model. GS is dead. So I'd guess that the IS and RC are the only platforms it would make it into unless the RX has a complete re-design for a totally different drive train configuration.

Still seems odd because the Rav4 Prime drive train would be faster than the current IS. And for the IS to be competitive going forward - it needs to be more like Model 3 speed, not Rav4 speed. Even the current Supra BMW turbo 6 isn't really even in the same ball park as a Model 3 performance. If the IS is going to survive another generation, it needs to be quicker than 5 second 0-60 times.