We'll see. I for one believe opening up the network will lure more customers into the Tesla fold. At the moment though, Tesla's bottleneck is still ramping up production, not landing new orders.
If their network is underutilized, they have an interest to open it. If their goal is to build a walled garden, they will not open it. So far the latter hypothesis matches the observations better.
In the US Tesla are the waste majority of EV, and those that are not Tesla usually can't charge anywhere close to fast enough for it to be reasonable to charge at a Supercharger.
The markets are just totally different. In the EU there are lots of cars that could use the Superchargers so you can make way more money there then in the US.
They always said eventually they would open it up to everybody. Its a balance between it being a selling point and making money from higher utilization.
It's not a good control since there are other differences between US and EU, most notably charging connectors standards and chargers per cars (US superchargers are more crowded than EU on average).
There is no EU directive that requires Tesla to make the charging network available to non-Tesla vehicles. Just that fast charging stations must support the CCS standard, which Tesla used in Europe for years already.
