Trust me, I never try a new OS without testing it thoroughly using Oracle VirtualBox! So is the case with bugs filled Technical Previews of Windows 10 as well. One of the annoyance I had with the builds was, the VirtualBox display driver failing to load/install when the extension packs are installed. That forced me to browse through multiple VirtuaBox forum entries and there were multiple suggestions (few of them using setextradata switch), and came across one of them suggesting, enabling the Virtual Machine with 3D enabled under display properties.
Does it work? Yes!
Currently I am using VirtualBox 4.3.26, the latest release with Hyper-V disabled over my Windows 8.1 as host and Windows 10 Technical Preview build 10061 as guest OS
Please find below the VM’s display settings