There shouldn't be much of an issue. Right now, apparently the blocks on Ships 1-3 don't come anywhere near capacity and it is only a couple blocks on each that even have a lot of players at once. I think there were at least 20 blocks per ship. We also can't really compare it to JP, since they are using Microsoft Azure for the servers in NA, which has a lot more capacity than JP does.
There were issues with CBT on Day 1, but after that fix, they were fine for the rest of CBT and there were no issues with server load at OBT launch or official launch on XBOX One. They might open up one ship if the current 3 get full too quickly, but there don't even really seem to be that many people that will play on NA servers, considering all of their social media only has a couple tens of thousands, rather than in the hundreds of thousands or millions of followers. As of the time of this post, all of their social media combined is 63,666. To potentially cut out repeat subscribers, it is best to go with the social platform with the most followers, which is twitter at 42,925. Not all of them will actually play or be on all the time, so there shouldn't be much to worry about