Oracle VM Virtualbox is a virtualization platform that already runs NetBSD guest machines fine.
However, there are a few fine tunings missing: mouse and graphics support, better integration via client tools (clipboard sharing, time synchronization), and maybe some possible optimizations.
FreeBSD is supported, and the sources are available. Note that the FreeBSD kernel code might have license problems.
As a start there is a pkg of the build tools in pkgsrc/wip already (an ancient version), and Valeriy Ushakov has patches for current VirtualBox sources and NetBSD 5, to get the build tools going.
Overall this project is a mixture of various kernel and userland tasks. For GSoC, some of these may be defined as optional - e.g. working X11 should be a target, but could be dropped if other things turn out to be more difficult than expected. A list of things to check and improve could include:
- time synchronization
- proper mouse integration within X (absolute coordinates)
- shared clipboard support
- higher video resolutions
- hardware acceleration (XVideo, DRI...)
You need a machine with hardware virtualization support (VT-x/Intel or AMD-V) for reasonable guest machine speed. Supporting NetBSD fast without this would be possible with a few tweaks, but is not part of this project (and maybe not even a reasonable goal beyound GSoC).