ASRock released a new firmware (Version 1.4) for its X299 Taichi CLX motherboard that brings support for RDIMMs. Standard DIMMs currently max out at 32GB per stick. However, there are two caveats.
ASRock's X299 Taichi CLX Mothboard Now Supports RDIMMs up to 256GB : Read more
ASRock's X299 Taichi CLX Mothboard Now Supports RDIMMs up to 256GB : Read more