Back when it was originally announced, I had thought data center travel would have been something that made sense to implement at the tail end of 5.x so that there would be months to break it in and fix issues to have it ready to ease things at the launch of 6.0. Instead, it was deprioritized to focus on the launch of 6.0 itself.
After the last couple of weeks, I'm starting to wonder, was that SE's biggest mistake with this launch? Due to the worldwide situation, server hardware is still hard to get ahold of, and travel restrictions would make actually setting up physical hardware on site difficult even if they had the hardware available. Cloud-based servers were explored and abandoned due to instability, performance, and cost issues. This new feature of data center travel, on the other hand, is likely software-based, or at least mostly software-based meaning that it, along with the optimizations they did do, was probably something SE could have done to ease the login queue problems.
In order to give myself to try out a male Viera look, I thought to first try it on a fresh character, so I don't waste a fantasia on something I don't end up liking. Given the situation on my usual datacenter (US) during times I normally can play, I ended up rolling the test character on a Japanese datacenter. Login queues during US primetime there have been trivial, like single to double digits. I don't think I've seen 100+ in queue, and usually log in within seconds.
Sure, there's latency, but it's not unplayable, especially not for the type of tasks MSQ gives you. I feel like people who just want to get the story done to prepare for the launch of the raids would have been quite happy to simply run on a different datacenter in the short term. Language barriers are likely less of a problem since trusts have proven effective for at least story clears of dungeons.
At the very least, I wonder if this means that the launch of 7.0 will benefit from allowing players to spread out across data centers to even out the load across all times of day? I'll probably try to make sure to prepare for the next launch by clearing out as much inventory as possible to make the experience of playing without retainers for long periods of time more bearable given that I expect retainers to be unavailable during data center travel just like with world visit.