I will offer a second take on the statement, "target opening date to be determined."
In the past, Tesla has tried to install Superchargers over a long stretch of highway over the shortest period of time. It is possible that the Supercharger team wants to identify the specific locations, obtain permits, and arrange for the construction crews to be able to complete the I94 stretch east of Billings and through North Dakota.
I posit that many of the overcrowded locations already had deals in place for possible expansion, so there is no need to identify new sites in those places. Moreover, with the skyrocketing popularity of Tesla, I would submit that there are new locations who want Superchargers on site, so negotiation is a breeze with the property owners. These situations make it easier for Tesla to get the ball rolling sooner.
However, I think that Tesla wants to streamline the I94 build out. It is certainly plausible that they already have a few locations selected with lease agreements agreed-to in principle, if not already signed. But they might be experiencing hiccups in a few others, and they do not know when all the locations will have agreements in place.
It does not make much sense to me to build Superchargers in Jamestown and Bismarck, for example, if they are going to be isolated from the rest of the country until the rest of the highway route has been determined.