My opinion, the aim is to be 'open' to a sufficient degree that governments provide opportunities to allow the network to grow at the same pace as other networks. If it's expensive and inconvenient to other brands and they choose to use an alternative network then that's just fine, it would seem that as permission and grid is provided at service stations there will be multiple networks.It is simply that if the aim is to ultimately open up the UK network beyond what is being trialled, then going forward it really needs to be capable of one car/one stall charging irrespective of make. It seems ludicrous to continue building and opening new installations that now have a known and limiting design flaw for all make charging.
Given Musk’s other interests, unless the decision to start opening up was done somewhat spur of the moment, you wouldn’t have thought it would have been rocket science to plan ahead for it.
Tesla plan to sell lots more cars, and need to keep growing the network otherwise it'll become more of a liability than a positive as their fleet grows. This is necessary to achieve that, and makes good business sense.