It's expected that VEGA20, when released, will get a new interface called XGMI, this is a high speed interconnect and can be seen along the ones of NVLINK, a much faster connector. Thanks to a new set of AMDGPU Linux driver patches this was discussed. 

XGMI would be a peer-to-peer high-speed interconnect and is based on Infinity Fabric, the unified way to communicate with everything or AMD, even the processors use this. XGMI is basically AMD's alternative to NVIDIA's NVLink for inter-connecting GPUs. The finding was spotted by Phoronix who spotted the new entry in a new AMDGPU Linux driver. They, for now, can be found on the amd-gfx list but will likely be queued via -next for introduction in the Linux 4.20~5.0 kernel as part of their latest Vega 20 enablement work.

Radeon Vega 20 Will Have XGMI Interconnect