What is the business case for Tesla Diners? I can only think of Tesla/EV drivers on road trip looking for a place along their route to kill time while recharging. That can't be that big enough of a market.
I think the longest we've spent at a Supercharger was maybe 20 mins. The charge rates really drop (like charging any battery), so it often makes more sense to just stop a couple times with a low battery and add another 100 miles of range in < 5-10 mins.
But I would hope that Tesla has much better data on their users to be able to determine how long people would stop, and where.
I would assume a better model might be locating the supercharger near a robust/successful location with plenty of restaurants and coffee shops.
but some superchargers are in pretty desolate areas - that might be a better place for "the company cafeteria"