All else equal you can charge batteries based on a % of their total capacity. Current superchargers can do about 2%/min for a model S in the 0-80% charge range but can't deliver the requisite power for a 400kwh pack. But I also haven't seen very many supercharger stations that would be particularly well suited for truck traffic either, so I'd imagine there will be a new charger/stations as well.
Sure batteries are no where near competing on absolute range of diesel but I don't think they have to. The question is can you get a days driving in without spending hours and hours charging while keeping the battery capital cost/weight reasonable.
You don't need a 1200kwh pack for that because you can take a couple short breaks plus a lunch with supercharging and over double your effective capacity.
We'll see what happens but I'd be very surprised if the announcement doesn't include a new super charger and stations unless they design it for short range point to point only.
[0]https://electrek.co/2016/11/14/tesla-model-3-battery-energy-...