QEMU was installed on the original Wii and was made to run Windows XP. Since 1GB of the Wii U RAM is dedicated to the system, we should have around 1GB free for this. It could definitely run XP. I also estimate that the 32-bit version of Windows Vista or 7 could possibly be run as well, albeit fairly slowly. That would be interesting to see for sure. Here is a video of Windows Vista running through QEMU on a PlayStation 3. According to IGN, the Wii U's PPC processor is about 50% more powerful than the PS3's cell processor. Whether or not that is completely factual, QEMU should eventually be able to run just fine. Of course, it would be way easier to run QEMU on the Wii U if there was a Linux implementation, which we seem to currently be pretty far from. You can read more about the specs of the Wii U here. DOSBox would be nice as well. On the 3DS, we had the RetroArch implementation for Windows 95, which you can see in my video here: The Wii U could definitely run DOS/Windows 95/98/etc. using DOSBox.