A VirtualBox ticket has been opened requesting a Gallium3D driver to replace their classic Mesa driver. Unfortunately, an Oracle developer's initial response was:
We discussed this internally, and we weren't convinced that it would gain us a lot. It would mean throwing away our existing DRI driver code (admittedly the existing code is not the nicest, but it works) and starting from scratch without any clear reason to think that the result would be better. In particular, since we pass on graphics pipeline commands and data to the host's OpenGL implementation it seemed that Gallium3D might actually be a worse fit.
If you know more about this then please feel free to add to this ticket of course.
This though wouldn't be the first Gallium3D driver for a virtualized platform but last year VMware (which owns Tungsten Graphics, the firm that initially developed this graphics driver architecture) announced a Gallium3D driver for its VMware virtualization stack and subsequently released the driver along with its new kernel DRM code.
By using a Gallium3D driver in the virtualization mix it provides the same benefits of being able to have a smaller, cleaner driver that's able to leverage more common code, but it also means that the virtualized guest can tap into any state tracker while having hardware acceleration for the host. Right now this mostly means OpenGL, OpenGL ES, and OpenVG, but there are state trackers for OpenCL, DirectX 10/11, VDPAU / XvMC, and EXA under development.
There's now a effort underway in our forums by the creator of this Gallium3D support ticket request to convince Oracle to back a Gallium3D driver for VirtualBox.