You mean when they announced World Visit was being added?
Now 3 years have passed, it would be interesting to find out what the outcome was on the player experience.
How many players ended up transferring worlds just for the sake of getting a house? Among those who transferred just to get a house, was it worth it?
How many players embraced their new world communities and how many choose to become "commuters" to continue playing with their friends on their old worlds (assuming they hadn't changed logical data centers)?
How long did it take for players who transferred to Spriggan and Twintania to feel like they were getting a game experience on par with what they had prior to transfer?
How long did it take for players on Light and Chaos to feel like duty queues and Party Finder normalized after the player population feeding matchmaking was effectively cut in half?
I don't know that all of that is a "dead certainty".
I think the only reason why Materia ended up with the 75/25 split was because they choose to implement the same split globally for Empyreum release. By the time the new EU worlds get added in July and the new NA data center/worlds get added in August, the ward split will likely be different from world to world.
I do expect them to keep housing locked for an extended period as you say. They didn't learn from Spriggan/Twintania when it came time to setting up Materia. They will not have learned from Materia when it comes time to set up EU/NA. It doesn't take 90 days to get a FC to rank 6. It takes 90 minutes with just a little advance prep collecting items for Expert Deliveries (been there, done that with my FC).
It's going to be a rocky start for the new EU worlds and new NA data center when there's no incentive to transfer existing characters. Housing stops being an incentive when it's withheld. Most players are after personal housing so there would be no reason to transfer until the week before housing is opened.