128GB for 3K; per the announcement their ConnectX networking allows two Project Digits devices to be plugged into eachother and work together as one device giving you 256GB for $6k, and, AFAIK, existing frameworks can split models across devices, as well, hence, presumably, the upthread suggestion that Project Digits would provide 512GB for $12k, though arguably the last step is cheating.
If you want to split tensorwise yes. Layerwise splits could go over Ethernet.
I would be interested to see how feasible hybrid approaches would be, e.g. connect each pair up directly via ConnectX and then connect the sets together via Ethernet.