Earlier quoted context omitted.
Not going to happen (despite my still being on 18.x) because they want to force you to upgrade to 26 for publicity. As simple as that. The new "security upgrade available" will (I bet) be "to 26".
> for publicity Or don’t want to maintain two different security architectures.
But they did push out iOS 18 patches for iPhone XR/XS, so the backporting work is already done. Seems like they want to force people to 26.