As with other expansions they'll add 3 instances to every zone and reinstate an idle timer so people can't afk all night. After SB they learned their lessons about instances and don't stick them in the beginning of the story arc anymore and they've made significant back end improvements, not the least of which was changing the DC structure to allow for more resources to be devoted to infrastructure stability.

There's no cure for having 10,000 people trying to log in at the same time, so you'll still have a queue when you log in but they've made improvements to make that faster and more stable as well. Queue times will resolve itself after the first week as people stop trying to rush the servers and go back to their normal routines.

Any MMO expansion launch will have its bumps but FF14 seems to handle it more smoothly than most.