Is Fedora Silverblue stateless?

Would you consider Fedora Silverblue similar to Intel ClearLinux, wherein it can be reset by deleting /etc and /var?

If not, does it plan to be something like that, having a full system reset function?

Similar, yes, as most of the configuration is part of the base image. You can run

# ostree admin config-diff

to see the modified files between your system’s configuration and the defaults.