This was bound to happen eventually. In order for Tesla to properly compete within a market growing with charging companies that support most EV models (including Tesla models via adapters), it had to open its own Superchargers up to these other brands as well.
Until now, Supercharging has been limited to Tesla vehicles within the US. However, later this year Tesla will be changing that by allowing support for other options. Nothing official has been announced by the company just yet. The details actually came from the White House via a fact-sheet posted online.
Drivers of non-Tesla vehicles will, of course, require an adapter and may not experience the full capabilities of the Supercharger’s charging times (compared to Tesla vehicles). However, it opens access to the market for vehicles that may not have alternative choices nearby. It’s the same for Tesla vehicles and third-party chargers.
It will likely be a slow roll-out, starting with a beta program that would allow Tesla to determine how much of an effect it would have on the network of chargers. The company likely wouldn’t want to lock up all of the available chargers from Tesla owners. Therefore, the transition may not be that noticable until later next year as it grows larger (if at all).
As the world continues to move toward adopting EVs over gas vehicles, there is going to be a huge demand for charging all over. A demand that current charging networks aren’t yet prepared for. They are capable of handling what is out there at this time, but a massive upgrade will be needed to keep up. Something, thankfully, that all companies (and the Whitehouse) are working hard to deliver on.