They have previously said they considered cloud servers and decided against them, because they are slower.

But in the live letter earlier, they just did not want a repeat of the issue of having to close sales and lock servers when an expansion launches because they felt bad about it.

They will be testing cloud servers in the 6.5x patches and they will put details of it on the lodestone as well. I am not sure how they are going about it but I suppose now that we have Data Center Travel, that if we have a large queue, what we could do is choose to DC travel to a temporary cloud server that exists temporarily to skip the queues when an expansion launches. Or they could mean there are some permanent cloud servers, I really don't know yet.