If going for implementing NUMA functionality for real, I'd probably suggest to limit the initial scope of this and start from properly returning NUMA associations from NtQuerySystemInformation( SystemLogicalProcessorInformation[Ex] ), so also existing GetLogicalProcessorInformationEx returns actual data.
Scratch that, the numa nodes are actually queried and filled already. And probably GetNumaProcessorNode() / GetNumaHighestNodeNumber() can be easily implemented on top of GetLogicalProcessorInformationEx().