With the population continuing to grow it might be smart to have separate US and EU servers. The large population is great, but its a pain to quest and you can't see mobs more than 12 yards in front of you.
I'm not sure if its possible, but you could host a US server in NA, giving NA players better pings, and convert the current server into an EU server. Offer players free transfers. Depending on how big this gets you could implement log in queues and more realms as needed.
My 2 cents