I'm really in support of everything that System76 is doing. Outside of Framework I think they're one of the more interesting enthusiast projects. I think what makes me particularly excited for Cosmic is that it will be under the GPL3 license, and that it will use GTK.
Mostly using tlp (there's also a gui flatpak for it) to manage sind knee power settings. But checkout this repo for other ideas/tweaks (you definitely don't need to use saltstack to do it but it shows what's possible): https://github.com/lightrush/framework-laptop-formula
It will not be using GTK for first party applets and applications. COSMIC is being built with libcosmic, which is a cosmic-themed widget library built on top of iced. The design team also has a collaboration with Slint so that Slint can be used to make applications with the same look and feel as libcosmic.