Well... he is now. Expect this to become the norm across the Big 2, they’ve been pushing hard that “anyone can wear the mask”. People will pretend it’s progressiveness but that’s not really why the suits are into it. The suits want it because it’s far less risky to simply establish these brands as mantles that can be passed from one person to the next, allowing them to constantly put out new movies using the same IP with much less risk of audience fatigue. Hollywood as a whole doesn’t take chances on new IP anymore, hence the endless reboots and nostalgia bait.
If this new reboot from Abrams is off in its own universe, I wouldn’t be surprised if WB attempted a soft reboot in the “main” DCEU universe with Jon as Superman. Yara could take over for Gadot, and since Dick is the dead Robin of the Snyderverse, and Bruce presumably never took on another, you could have Jace Fox or Batgirl take over for Bruce Batman instead. I expect Supergirl to fill the hole left by Cavill in the main universe, but I wouldn’t be surprised if the reason why WB ok’d pushing Jon when there is seemingly no plans to feature him anywhere, is because they’re eyeing him up as a way to reboot “mainline” Superman.