Martin committed a nifty improvement to packages a few days ago, but neglected to announce it here, so I'm filling in. You now set the toolchain tuple in config.mk in rumprun-packages root (see config.mk.dist). Then, everything just builds with "make" without having to remember to "make CC=foo-rumprun-netbsdbar". Notably, you still need to bake the binaries yourself. I don't think we can automate the baking step without making things too simple (i.e. wrong).
For now, if you want to compile for multiple architectures, it's easiest to have several clones of rumprun-packages. Still looking for the real packaging system ...
Additionally, Krishna has packaged some key-value stores such as LevelDB and Redis (and is working on more?). I think rumprun is particularly suited for that type of networki-server purpose, so keep up the good work!