I am wondering if there are any other EU states that subsidize religious groups the way Norway does. The WTS will challenge this ruling because it could cause a cascade effect, and if there are any other nations that pay you for being a religion, they stand to lose out on that money.
But this will also be used by them for PR. "Look at how they oppress us! Just as we predicted before the end!" Meanwhile, the main effect is that they can't sign official marriage documents. They can still have a fancy wedding celebration with all of the trappings, but they can't make it official. This slightest of inconveniences is the price they will pay. And they will paint it as persecution that proves the last days are almost over (yet again).
It's a weird way to encourage people to join, though. "Become part of our non-religion before it's too late!"