Due to the license required fro Windows Server 2012, it should be a per-node file. The current limitation, due to the fact that we do not have tools to edit the WinPE image once it is generate, requires the file to be present in a fixed location. Using a volume license, any number of nodes can be deployed at the same time (using same license key) while if the license is per-node (retail license) the nodes will have to be deployed sequentially, one after the other has finished installing. If support for WinPE image editing from Linux will be included at a later stage, the location of the unattended.xml file could be changed to the per-node path at that moment.