The first guide that includes 2012 R2 RTM versions of System Center and Windows Server is out. You can download it now and save it to be prepared to test certain scenarios when GA availability of R2 wave arrives.
Even though SC 2012 R2 and WS 2012 R2 are not released yet Microsoft published a guide to setup lab for Hyper-V Network Virtualization. There are no screenshot in the guide but you can have a sneak peak preview of the architecture of the new Multi-Tenant NVGRE Gateway. Check it out here.