Hi Patrick, thank you for your suggestion.
as Rag uses DPR’s pretrained weights as a submodule, so I made a TFDPR PR first. Now it’s around 25% progress on TFRag … I hope I can make a TFRag PR before EMNLP , and I will seek your suggestions on TFRag for sure 
Just in case you are interested in, my current draft with TFRagModel is here 3