Not sure how big your plans are.
My thoughts would be to start as a cmake generator but to eventually replace it. Maybe optionally.
And to integrate suppoet for existing package managers like vcpkg.
At the same time, I'd want to remain modular enough that's it's not all or nothing. I also don't like locking.
But right now package management and build system are decoupled completely. And they are not like that in other ecosystems.
For example, Cmake can use vcpkg to install a package but then I still have to write more cmake to actually find and use it.