Work is ongoing to bring this modern toolchain to all other ports too (most of them already work, but some more testing will be done). If you want to try it, just add -V HAVE_GCC=48 to the build.sh invocation.
Note that in parallel clang is available as an alternative option for a few architectures already (i386, amd64, arm, and sparc64), but needs more testing and debugging at least on some of them (e.g. the sparc64 kernel does not boot).
For a project with diverse hardware support like NetBSD, all toolchain updates are a big pain - so a big THANK YOU! to everyone involved; in no particular order Christos Zoulas, matthew green, Nick Hudson, Tohru Nishimura, Frank Wille (and myself).