The interest from other automakers is irrelevant, because that's expected. No car maker is going to cooperate with any other in a way that makes the other look good. BMW electric car owners could desperately want to use the supercharger network, but there is no way in hell BMW would ever let them.
They would if the basis for all of it were open standards. Many car components are standard sizes and can be used regardless of manufacturer. However because it is a proprietary standard and Tesla leads in adoption car manufacturers would be susceptible to the embrace and extend tactic. They would never stand for that.
