Details of new large scale content will be revealed in part 2. The new GATE is basically like a roller-coaster with you sitting in Air Force (from Sigmascape) and shooting things.
They did not reveal the new client.
More details about the World Visit system were given at the Live Letter
It's as simple as clicking on one of the three Aetherytes and selecting the World you wish to visit. A new window will pop much like Duty Finder. Data Center has to check the congestion of the World you plan to visit.
Finer details of the restriction:
Needless to say, the majority of the reaction upon hearing that Blue Mage was designed for Solo Play in an MMORPG was not received well by many on Twitch Chat. The reception in the hall was lukewarm at best. With many hard instance restrictions in place, is the job already dead even before its launch? Many believe so.
Part of the reason for the design decision is that the Blue Mage may not have the necessary skills for party play. Yoshi P attempted to defend the design decision with an example:
"Imagine a Blue Mage in Omega M and F successfully casting Lv.5 Death. The fight will be over instantly and therefore breaking the game. This wouldn't be fun for anyone."
Though I agree with this example, I believe there could have been a way around this such as making the boss immune to such skills. I do hope come 4.5 that my skepticism over this job is proven to be unfounded or completely baseless.