You’re on the Fedora forums so you’ll get answers from the community here, not from Red Hat or IBM. If you want their opinions, you should ask them directly. I’m a Red Hat employee but I can’t speak for either Red Hat or IBM. I can only speak as a Fedora community member.
Fedora image based variants (Atomic Desktops, CoreOS, IoT, bootc, etc.) are all built from Fedora packages. So by definition, they can not replace other Fedora variants, because those will likely keep existing as long as Fedora packages exists. Image based variants also don’t need to replace the other ones to be successful (and I would argue that we already are kind of successful).