"The first car to feature the new infotainment system will be the new 2018 Toyota Camry, which is*already on sale in the US. The first Mazda to use this system will likely be the redesigned Mazda 3,*which is expected in 2018. It's still not confirmed when this system will start appearing on other vehicles from these manufacturers, but reports indicated that it will be rolled out in stages. We should point out that while Toyota and Mazda will share a system, this only refers to the platform on which it's built. Mazda's version should look very different, and each company will be responsible for developing new features and applications"
And Mazdas will debut in 18 on the 3. That's more in line with the supposed leak mentioned on Reddit.
Here's an article from CNET that confirms what 7 is saying:
https://www.cnet.com/google-amp/news/toyota-mazda-to-share-next-gen-infotainment-platform/
Toyota and Mazda only recently announced their partnership, but the first fruits of their labor will be seen very soon.
Future Mazda and Toyota models will share the same infotainment underpinnings as part of a joint development effort, Nikkei reports. Toyota first developed the Linux-based guts of its new Entune 3.0 infotainment system, but it brought in Mazda for additional streamlining because of a lack of software developers in Japan's auto industry.
The system will first reach the public by way of the 2018 Toyota Camry, which is already on sale in the US. It should land in Mazda's stable when the redesigned Mazda3 debuts in the near future, although that has not been officially confirmed. Nikkei claims other vehicles from these manufacturers will receive the updated platform in stages.
Now, bear in mind this doesn't refer to the whole infotainment system, this only covers the platform off which it's built. Mazda's version will undoubtedly look different, and each company will be responsible for developing the features and applications that will live in each system.
Both systems, though, will be able to make use of Toyota's new Wi-Fi hotspot, which utilizes a cellular network connection to deliver over-the-air updates and new apps without requiring the owner to provide the connection. Toyota's hotspot can accommodate up to five devices simultaneously on the 2018 Camry.
While this new infotainment system will be rather flexible thanks to a library of available third-party apps like Slacker or Pandora, it should be noted that the system still does not support Apple CarPlay or Android Auto -- or, at least it doesn't on the 2018 Toyota Camry. Hopefully that will change with other models, but Toyota has a historical aversion to this sort of phone mirroring.