gcc-16 is now packaged as a first attempt, please see deb https://people.debian.org/~doko/tmp/gcc-16 ./Not uploading for experimental, because there are still some foreseeable soname bumps for various runtime libraries.
As long as this is not yet in the archive, please report bugs under the gcc-snapshot package.
For a little more architecture support, please also see the package in https://launchpad.net/~ubuntu-toolchain-r/+archive/ubuntu/test Matthias